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 $53.49   4.205%   $55.7393   $55.74   $55.75   $55.70  
  Purchase #2 $167.33   7.427%   $179.7576   $179.76   $179.75   $179.80  
  Purchase #3 $100.26   6.119%   $106.3949   $106.39   $106.40   $106.40  
  Purchase #4 $204.91   3.738%   $212.5695   $212.57   $212.55   $212.60  
  Purchase #5 $61.81   13.257%   $70.0042   $70.00   $70.00   $70.00  
  Purchase #6 $73.99   3.872%   $76.8549   $76.85   $76.85   $76.90  
  Purchase #7 $139.35   7.644%   $150.0019   $150.00   $150.00   $150.00  
  7 purchase totals = $801.14       $851.3223   $851.31   $851.30   $851.40