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 $91.98   10.242%   $101.4006   $101.40   $101.40   $101.40  
  Purchase #2 $228.92   9.593%   $250.8803   $250.88   $250.90   $250.90  
  Purchase #3 $10.27   13.774%   $11.6846   $11.68   $11.70   $11.70  
  Purchase #4 $60.52   3.408%   $62.5825   $62.58   $62.60   $62.60  
  Purchase #5 $118.77   12.142%   $133.1911   $133.19   $133.20   $133.20  
  Purchase #6 $44.56   11.734%   $49.7887   $49.79   $49.80   $49.80  
  Purchase #7 $216.32   11.428%   $241.041   $241.04   $241.05   $241.00  
  7 purchase totals = $771.34       $850.5688   $850.56   $850.65   $850.60