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 $111.80   5.586%   $118.0451   $118.05   $118.05   $118.00  
  Purchase #2 $167.71   7.491%   $180.2732   $180.27   $180.25   $180.30  
  Purchase #3 $129.65   7.768%   $139.7212   $139.72   $139.70   $139.70  
  Purchase #4 $11.51   3.534%   $11.9168   $11.92   $11.90   $11.90  
  Purchase #5 $246.55   5.842%   $260.9535   $260.95   $260.95   $261.00  
  Purchase #6 $98.31   7.830%   $106.0077   $106.01   $106.00   $106.00  
  Purchase #7 $49.46   5.400%   $52.1308   $52.13   $52.15   $52.10  
  7 purchase totals = $814.99       $869.0483   $869.05   $869.00   $869.00