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 $181.80   11.486%   $202.6815   $202.68   $202.70   $202.70  
  Purchase #2 $30.89   7.584%   $33.2327   $33.23   $33.25   $33.20  
  Purchase #3 $170.32   3.797%   $176.7871   $176.79   $176.80   $176.80  
  Purchase #4 $38.82   13.823%   $44.1861   $44.19   $44.20   $44.20  
  Purchase #5 $122.98   8.118%   $132.9635   $132.96   $132.95   $133.00  
  Purchase #6 $88.28   9.553%   $96.7134   $96.71   $96.70   $96.70  
  Purchase #7 $171.72   6.363%   $182.6465   $182.65   $182.65   $182.60  
  7 purchase totals = $804.81       $869.2108   $869.21   $869.25   $869.20