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 $20.42   3.322%   $21.0984   $21.10   $21.10   $21.10  
  Purchase #2 $76.70   13.800%   $87.2846   $87.28   $87.30   $87.30  
  Purchase #3 $125.47   13.268%   $142.1174   $142.12   $142.10   $142.10  
  Purchase #4 $107.28   9.576%   $117.5531   $117.55   $117.55   $117.60  
  Purchase #5 $39.62   3.849%   $41.145   $41.15   $41.15   $41.10  
  Purchase #6 $143.48   5.135%   $150.8477   $150.85   $150.85   $150.80  
  Purchase #7 $195.25   11.691%   $218.0767   $218.08   $218.10   $218.10  
  7 purchase totals = $708.22       $778.1229   $778.13   $778.15   $778.10