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 $174.97   5.273%   $184.1962   $184.20   $184.20   $184.20  
  Purchase #2 $36.57   6.342%   $38.8893   $38.89   $38.90   $38.90  
  Purchase #3 $11.92   6.263%   $12.6665   $12.67   $12.65   $12.70  
  Purchase #4 $19.83   11.619%   $22.134   $22.13   $22.15   $22.10  
  Purchase #5 $120.30   10.860%   $133.3646   $133.36   $133.35   $133.40  
  Purchase #6 $53.95   12.804%   $60.8578   $60.86   $60.85   $60.90  
  Purchase #7 $250.38   11.820%   $279.9749   $279.97   $279.95   $280.00  
  7 purchase totals = $667.92       $732.0833   $732.08   $732.05   $732.20