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 $233.29   13.482%   $264.7422   $264.74   $264.75   $264.70  
  Purchase #2 $54.58   12.307%   $61.2972   $61.30   $61.30   $61.30  
  Purchase #3 $32.97   3.434%   $34.1022   $34.10   $34.10   $34.10  
  Purchase #4 $65.69   4.308%   $68.5199   $68.52   $68.50   $68.50  
  Purchase #5 $95.29   3.326%   $98.4593   $98.46   $98.45   $98.50  
  Purchase #6 $204.43   12.661%   $230.3129   $230.31   $230.30   $230.30  
  Purchase #7 $25.59   9.272%   $27.9627   $27.96   $27.95   $28.00  
  7 purchase totals = $711.84       $785.3964   $785.39   $785.35   $785.40