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 $83.56   10.731%   $92.5268   $92.53   $92.55   $92.50  
  Purchase #2 $114.69   7.641%   $123.4535   $123.45   $123.45   $123.50  
  Purchase #3 $228.50   13.206%   $258.6757   $258.68   $258.70   $258.70  
  Purchase #4 $8.52   8.285%   $9.2259   $9.23   $9.25   $9.20  
  Purchase #5 $206.92   12.349%   $232.4726   $232.47   $232.45   $232.50  
  Purchase #6 $113.33   11.425%   $126.278   $126.28   $126.30   $126.30  
  Purchase #7 $26.33   12.864%   $29.7171   $29.72   $29.70   $29.70  
  7 purchase totals = $781.85       $872.3496   $872.36   $872.40   $872.40