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 $211.69   6.297%   $225.0201   $225.02   $225.00   $225.00  
  Purchase #2 $80.53   5.464%   $84.9302   $84.93   $84.95   $84.90  
  Purchase #3 $216.33   6.400%   $230.1751   $230.18   $230.20   $230.20  
  Purchase #4 $110.47   3.549%   $114.3906   $114.39   $114.40   $114.40  
  Purchase #5 $71.44   4.809%   $74.8755   $74.88   $74.90   $74.90  
  Purchase #6 $115.31   11.484%   $128.5522   $128.55   $128.55   $128.60  
  Purchase #7 $197.31   5.606%   $208.3712   $208.37   $208.35   $208.40  
  7 purchase totals = $1,003.08       $1,066.3149   $1,066.32   $1,066.35   $1,066.40