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 $92.28   3.309%   $95.3335   $95.33   $95.35   $95.30  
  Purchase #2 $80.32   10.786%   $88.9833   $88.98   $89.00   $89.00  
  Purchase #3 $158.85   7.198%   $170.284   $170.28   $170.30   $170.30  
  Purchase #4 $142.68   9.121%   $155.6938   $155.69   $155.70   $155.70  
  Purchase #5 $60.63   10.430%   $66.9537   $66.95   $66.95   $67.00  
  Purchase #6 $142.72   9.173%   $155.8117   $155.81   $155.80   $155.80  
  Purchase #7 $204.28   11.356%   $227.478   $227.48   $227.50   $227.50  
  7 purchase totals = $881.76       $960.5380   $960.52   $960.60   $960.60