Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $97.59   5.541%   $102.9975   $103.00   $103.00   $103.00  
  Purchase #2 $221.26   11.488%   $246.6783   $246.68   $246.70   $246.70  
  Purchase #3 $240.26   9.450%   $262.9646   $262.96   $262.95   $263.00  
  Purchase #4 $147.47   11.419%   $164.3096   $164.31   $164.30   $164.30  
  Purchase #5 $163.98   10.568%   $181.3094   $181.31   $181.30   $181.30  
  Purchase #6 $196.55   12.859%   $221.8244   $221.82   $221.80   $221.80  
  Purchase #7 $188.37   12.743%   $212.374   $212.37   $212.35   $212.40  
  7 purchase totals = $1,255.48       $1,392.4578   $1,392.45   $1,392.40   $1,392.50