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 $141.52   5.681%   $149.5598   $149.56   $149.55   $149.60  
  Purchase #2 $242.54   13.437%   $275.1301   $275.13   $275.15   $275.10  
  Purchase #3 $241.71   9.560%   $264.8175   $264.82   $264.80   $264.80  
  Purchase #4 $59.47   10.180%   $65.524   $65.52   $65.50   $65.50  
  Purchase #5 $178.63   4.381%   $186.4558   $186.46   $186.45   $186.50  
  Purchase #6 $111.47   6.775%   $119.0221   $119.02   $119.00   $119.00  
  Purchase #7 $208.84   12.415%   $234.7675   $234.77   $234.75   $234.80  
  7 purchase totals = $1,184.18       $1,295.2768   $1,295.28   $1,295.20   $1,295.30