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 $212.74   13.499%   $241.4578   $241.46   $241.45   $241.50  
  Purchase #2 $22.78   7.722%   $24.5391   $24.54   $24.55   $24.50  
  Purchase #3 $10.52   7.363%   $11.2946   $11.29   $11.30   $11.30  
  Purchase #4 $208.26   12.722%   $234.7548   $234.75   $234.75   $234.80  
  Purchase #5 $153.57   10.854%   $170.2385   $170.24   $170.25   $170.20  
  Purchase #6 $189.91   10.578%   $209.9987   $210.00   $210.00   $210.00  
  Purchase #7 $226.31   5.314%   $238.3361   $238.34   $238.35   $238.30  
  7 purchase totals = $1,024.09       $1,130.6196   $1,130.62   $1,130.65   $1,130.60