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 $80.76   13.331%   $91.5261   $91.53   $91.55   $91.50  
  Purchase #2 $107.73   12.421%   $121.1111   $121.11   $121.10   $121.10  
  Purchase #3 $232.64   8.337%   $252.0352   $252.04   $252.05   $252.00  
  Purchase #4 $108.32   8.516%   $117.5445   $117.54   $117.55   $117.50  
  Purchase #5 $44.80   12.300%   $50.3104   $50.31   $50.30   $50.30  
  Purchase #6 $106.28   4.862%   $111.4473   $111.45   $111.45   $111.40  
  Purchase #7 $142.65   6.193%   $151.4843   $151.48   $151.50   $151.50  
  7 purchase totals = $823.18       $895.4589   $895.46   $895.50   $895.30