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 $232.93   8.263%   $252.177   $252.18   $252.20   $252.20  
  Purchase #2 $209.84   11.786%   $234.5717   $234.57   $234.55   $234.60  
  Purchase #3 $38.98   9.256%   $42.588   $42.59   $42.60   $42.60  
  Purchase #4 $102.89   12.872%   $116.134   $116.13   $116.15   $116.10  
  Purchase #5 $206.70   12.710%   $232.9716   $232.97   $232.95   $233.00  
  Purchase #6 $98.90   10.113%   $108.9018   $108.90   $108.90   $108.90  
  Purchase #7 $156.85   4.785%   $164.3553   $164.36   $164.35   $164.40  
  7 purchase totals = $1,047.09       $1,151.6994   $1,151.70   $1,151.70   $1,151.80