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 $155.30   12.803%   $175.1831   $175.18   $175.20   $175.20  
  Purchase #2 $36.72   7.163%   $39.3503   $39.35   $39.35   $39.40  
  Purchase #3 $178.89   8.419%   $193.9507   $193.95   $193.95   $194.00  
  Purchase #4 $157.73   11.365%   $175.656   $175.66   $175.65   $175.70  
  Purchase #5 $186.37   8.362%   $201.9543   $201.95   $201.95   $202.00  
  Purchase #6 $69.28   8.296%   $75.0275   $75.03   $75.05   $75.00  
  Purchase #7 $230.37   12.411%   $258.9612   $258.96   $258.95   $259.00  
  7 purchase totals = $1,014.66       $1,120.0831   $1,120.08   $1,120.10   $1,120.30