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 $68.44   9.551%   $74.9767   $74.98   $75.00   $75.00  
  Purchase #2 $195.78   7.796%   $211.043   $211.04   $211.05   $211.00  
  Purchase #3 $43.49   7.118%   $46.5856   $46.59   $46.60   $46.60  
  Purchase #4 $92.35   8.842%   $100.5156   $100.52   $100.50   $100.50  
  Purchase #5 $59.72   8.236%   $64.6385   $64.64   $64.65   $64.60  
  Purchase #6 $226.34   11.870%   $253.2066   $253.21   $253.20   $253.20  
  Purchase #7 $147.79   12.372%   $166.0746   $166.07   $166.05   $166.10  
  7 purchase totals = $833.91       $917.0406   $917.05   $917.05   $917.00