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 $246.48   11.561%   $274.9756   $274.98   $275.00   $275.00  
  Purchase #2 $155.57   12.764%   $175.427   $175.43   $175.45   $175.40  
  Purchase #3 $142.94   3.694%   $148.2202   $148.22   $148.20   $148.20  
  Purchase #4 $147.30   11.718%   $164.5606   $164.56   $164.55   $164.60  
  Purchase #5 $244.68   5.206%   $257.418   $257.42   $257.40   $257.40  
  Purchase #6 $250.98   11.423%   $279.6494   $279.65   $279.65   $279.60  
  Purchase #7 $152.54   6.555%   $162.539   $162.54   $162.55   $162.50  
  7 purchase totals = $1,340.49       $1,462.7898   $1,462.80   $1,462.80   $1,462.70