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 $81.56   8.134%   $88.1941   $88.19   $88.20   $88.20  
  Purchase #2 $167.25   11.469%   $186.4319   $186.43   $186.45   $186.40  
  Purchase #3 $235.52   4.523%   $246.1726   $246.17   $246.15   $246.20  
  Purchase #4 $53.79   12.488%   $60.5073   $60.51   $60.50   $60.50  
  Purchase #5 $163.84   11.257%   $182.2835   $182.28   $182.30   $182.30  
  Purchase #6 $173.74   5.122%   $182.639   $182.64   $182.65   $182.60  
  Purchase #7 $160.70   6.802%   $171.6308   $171.63   $171.65   $171.60  
  7 purchase totals = $1,036.40       $1,117.8592   $1,117.85   $1,117.90   $1,117.80