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 $212.89   11.118%   $236.5591   $236.56   $236.55   $236.60  
  Purchase #2 $103.96   6.720%   $110.9461   $110.95   $110.95   $110.90  
  Purchase #3 $126.78   7.568%   $136.3747   $136.37   $136.35   $136.40  
  Purchase #4 $188.93   5.560%   $199.4345   $199.43   $199.45   $199.40  
  Purchase #5 $104.69   3.219%   $108.06   $108.06   $108.05   $108.10  
  Purchase #6 $158.60   11.461%   $176.7771   $176.78   $176.80   $176.80  
  Purchase #7 $106.35   4.223%   $110.8412   $110.84   $110.85   $110.80  
  7 purchase totals = $1,002.20       $1,078.9927   $1,078.99   $1,079.00   $1,079.00