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 $65.87   12.305%   $73.9753   $73.98   $74.00   $74.00  
  Purchase #2 $168.71   7.684%   $181.6737   $181.67   $181.65   $181.70  
  Purchase #3 $155.83   4.684%   $163.1291   $163.13   $163.15   $163.10  
  Purchase #4 $211.33   13.587%   $240.0434   $240.04   $240.05   $240.00  
  Purchase #5 $44.39   9.411%   $48.5675   $48.57   $48.55   $48.60  
  Purchase #6 $196.67   11.512%   $219.3107   $219.31   $219.30   $219.30  
  Purchase #7 $146.88   6.744%   $156.7856   $156.79   $156.80   $156.80  
  7 purchase totals = $989.68       $1,083.4853   $1,083.49   $1,083.50   $1,083.50