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 $81.86   3.530%   $84.7497   $84.75   $84.75   $84.70  
  Purchase #2 $56.92   10.575%   $62.9393   $62.94   $62.95   $62.90  
  Purchase #3 $39.58   8.599%   $42.9835   $42.98   $43.00   $43.00  
  Purchase #4 $212.65   7.527%   $228.6562   $228.66   $228.65   $228.70  
  Purchase #5 $138.50   3.570%   $143.4445   $143.44   $143.45   $143.40  
  Purchase #6 $185.46   9.468%   $203.0194   $203.02   $203.00   $203.00  
  Purchase #7 $46.67   9.577%   $51.1396   $51.14   $51.15   $51.10  
  7 purchase totals = $761.64       $816.9322   $816.93   $816.95   $816.80