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 $40.79   8.689%   $44.3342   $44.33   $44.35   $44.30  
  Purchase #2 $81.96   5.263%   $86.2736   $86.27   $86.25   $86.30  
  Purchase #3 $178.25   13.618%   $202.5241   $202.52   $202.50   $202.50  
  Purchase #4 $21.35   8.573%   $23.1803   $23.18   $23.20   $23.20  
  Purchase #5 $195.73   11.789%   $218.8046   $218.80   $218.80   $218.80  
  Purchase #6 $232.49   13.123%   $262.9997   $263.00   $263.00   $263.00  
  Purchase #7 $14.86   8.746%   $16.1597   $16.16   $16.15   $16.20  
  7 purchase totals = $765.43       $854.2762   $854.26   $854.25   $854.30