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 $76.96   10.724%   $85.2132   $85.21   $85.20   $85.20  
  Purchase #2 $226.89   8.461%   $246.0872   $246.09   $246.10   $246.10  
  Purchase #3 $94.27   3.773%   $97.8268   $97.83   $97.85   $97.80  
  Purchase #4 $91.65   4.820%   $96.0675   $96.07   $96.05   $96.10  
  Purchase #5 $163.34   4.443%   $170.5972   $170.60   $170.60   $170.60  
  Purchase #6 $95.34   3.809%   $98.9715   $98.97   $98.95   $99.00  
  Purchase #7 $186.36   8.279%   $201.7887   $201.79   $201.80   $201.80  
  7 purchase totals = $934.81       $996.5521   $996.56   $996.55   $996.60