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 $55.70   10.144%   $61.3502   $61.35   $61.35   $61.40  
  Purchase #2 $112.55   3.561%   $116.5579   $116.56   $116.55   $116.60  
  Purchase #3 $183.89   11.463%   $204.9693   $204.97   $204.95   $205.00  
  Purchase #4 $125.82   7.673%   $135.4742   $135.47   $135.45   $135.50  
  Purchase #5 $154.69   4.593%   $161.7949   $161.79   $161.80   $161.80  
  Purchase #6 $227.59   12.670%   $256.4257   $256.43   $256.45   $256.40  
  Purchase #7 $165.76   5.549%   $174.958   $174.96   $174.95   $175.00  
  7 purchase totals = $1,026.00       $1,111.5302   $1,111.53   $1,111.50   $1,111.70