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 $220.27   6.352%   $234.2616   $234.26   $234.25   $234.30  
  Purchase #2 $46.74   6.240%   $49.6566   $49.66   $49.65   $49.70  
  Purchase #3 $145.98   4.349%   $152.3287   $152.33   $152.35   $152.30  
  Purchase #4 $117.42   12.779%   $132.4251   $132.43   $132.45   $132.40  
  Purchase #5 $39.95   11.567%   $44.571   $44.57   $44.55   $44.60  
  Purchase #6 $11.42   8.534%   $12.3946   $12.39   $12.40   $12.40  
  Purchase #7 $196.88   5.313%   $207.3402   $207.34   $207.35   $207.30  
  7 purchase totals = $778.66       $832.9778   $832.98   $833.00   $833.00