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 $203.94   11.854%   $228.115   $228.12   $228.10   $228.10  
  Purchase #2 $28.42   9.831%   $31.214   $31.21   $31.20   $31.20  
  Purchase #3 $87.62   11.203%   $97.4361   $97.44   $97.45   $97.40  
  Purchase #4 $245.61   12.867%   $277.2126   $277.21   $277.20   $277.20  
  Purchase #5 $6.87   8.158%   $7.4305   $7.43   $7.45   $7.40  
  Purchase #6 $145.27   8.701%   $157.9099   $157.91   $157.90   $157.90  
  Purchase #7 $59.38   13.238%   $67.2407   $67.24   $67.25   $67.20  
  7 purchase totals = $777.11       $866.5588   $866.56   $866.55   $866.40