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 $45.25   9.661%   $49.6216   $49.62   $49.60   $49.60  
  Purchase #2 $224.32   11.739%   $250.6529   $250.65   $250.65   $250.70  
  Purchase #3 $110.63   5.775%   $117.0189   $117.02   $117.00   $117.00  
  Purchase #4 $126.84   9.209%   $138.5207   $138.52   $138.50   $138.50  
  Purchase #5 $230.92   12.206%   $259.1061   $259.11   $259.10   $259.10  
  Purchase #6 $100.35   7.465%   $107.8411   $107.84   $107.85   $107.80  
  Purchase #7 $87.78   8.685%   $95.4037   $95.40   $95.40   $95.40  
  7 purchase totals = $926.09       $1,018.1650   $1,018.16   $1,018.10   $1,018.10