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 $200.94   13.141%   $227.3455   $227.35   $227.35   $227.30  
  Purchase #2 $87.57   13.589%   $99.4699   $99.47   $99.45   $99.50  
  Purchase #3 $119.78   12.667%   $134.9525   $134.95   $134.95   $135.00  
  Purchase #4 $63.26   3.589%   $65.5304   $65.53   $65.55   $65.50  
  Purchase #5 $203.67   12.124%   $228.363   $228.36   $228.35   $228.40  
  Purchase #6 $150.66   7.498%   $161.9565   $161.96   $161.95   $162.00  
  Purchase #7 $215.57   11.817%   $241.0439   $241.04   $241.05   $241.00  
  7 purchase totals = $1,041.45       $1,158.6617   $1,158.66   $1,158.65   $1,158.70