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 $95.67   8.630%   $103.9263   $103.93   $103.95   $103.90  
  Purchase #2 $91.85   13.577%   $104.3205   $104.32   $104.30   $104.30  
  Purchase #3 $192.67   10.459%   $212.8214   $212.82   $212.80   $212.80  
  Purchase #4 $6.29   10.467%   $6.9484   $6.95   $6.95   $6.90  
  Purchase #5 $152.80   5.704%   $161.5157   $161.52   $161.50   $161.50  
  Purchase #6 $96.51   12.795%   $108.8585   $108.86   $108.85   $108.90  
  Purchase #7 $85.43   10.586%   $94.4736   $94.47   $94.45   $94.50  
  7 purchase totals = $721.22       $792.8644   $792.87   $792.80   $792.80