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 $58.51   4.517%   $61.1529   $61.15   $61.15   $61.20  
  Purchase #2 $99.85   8.123%   $107.9608   $107.96   $107.95   $108.00  
  Purchase #3 $216.39   13.807%   $246.267   $246.27   $246.25   $246.30  
  Purchase #4 $241.49   12.363%   $271.3454   $271.35   $271.35   $271.30  
  Purchase #5 $124.84   4.578%   $130.5552   $130.56   $130.55   $130.60  
  Purchase #6 $53.92   5.539%   $56.9066   $56.91   $56.90   $56.90  
  Purchase #7 $43.82   11.277%   $48.7616   $48.76   $48.75   $48.80  
  7 purchase totals = $838.82       $922.9495   $922.96   $922.90   $923.10