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 $32.54   4.468%   $33.9939   $33.99   $34.00   $34.00  
  Purchase #2 $217.96   8.150%   $235.7237   $235.72   $235.70   $235.70  
  Purchase #3 $206.48   9.594%   $226.2897   $226.29   $226.30   $226.30  
  Purchase #4 $55.87   6.113%   $59.2853   $59.29   $59.30   $59.30  
  Purchase #5 $92.95   9.761%   $102.0228   $102.02   $102.00   $102.00  
  Purchase #6 $17.88   10.454%   $19.7492   $19.75   $19.75   $19.70  
  Purchase #7 $75.52   10.599%   $83.5244   $83.52   $83.50   $83.50  
  7 purchase totals = $699.20       $760.5890   $760.58   $760.55   $760.50