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 $24.48   4.791%   $25.6528   $25.65   $25.65   $25.70  
  Purchase #2 $84.68   13.865%   $96.4209   $96.42   $96.40   $96.40  
  Purchase #3 $25.68   5.316%   $27.0451   $27.05   $27.05   $27.00  
  Purchase #4 $118.54   11.467%   $132.133   $132.13   $132.15   $132.10  
  Purchase #5 $48.26   12.835%   $54.4542   $54.45   $54.45   $54.50  
  Purchase #6 $228.29   7.385%   $245.1492   $245.15   $245.15   $245.10  
  Purchase #7 $247.35   12.325%   $277.8359   $277.84   $277.85   $277.80  
  7 purchase totals = $777.28       $858.6911   $858.69   $858.70   $858.60