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 $60.96   12.633%   $68.6611   $68.66   $68.65   $68.70  
  Purchase #2 $239.28   12.514%   $269.2235   $269.22   $269.20   $269.20  
  Purchase #3 $246.94   11.586%   $275.5505   $275.55   $275.55   $275.60  
  Purchase #4 $120.38   4.309%   $125.5672   $125.57   $125.55   $125.60  
  Purchase #5 $58.77   11.109%   $65.2988   $65.30   $65.30   $65.30  
  Purchase #6 $148.27   7.265%   $159.0418   $159.04   $159.05   $159.00  
  Purchase #7 $241.42   6.203%   $256.3953   $256.40   $256.40   $256.40  
  7 purchase totals = $1,116.02       $1,219.7382   $1,219.74   $1,219.70   $1,219.80