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 $178.79   12.576%   $201.2746   $201.27   $201.25   $201.30  
  Purchase #2 $219.63   9.818%   $241.1933   $241.19   $241.20   $241.20  
  Purchase #3 $231.65   11.137%   $257.4489   $257.45   $257.45   $257.40  
  Purchase #4 $163.93   6.493%   $174.574   $174.57   $174.55   $174.60  
  Purchase #5 $102.93   11.832%   $115.1087   $115.11   $115.10   $115.10  
  Purchase #6 $152.31   6.171%   $161.7091   $161.71   $161.70   $161.70  
  Purchase #7 $192.96   11.577%   $215.299   $215.30   $215.30   $215.30  
  7 purchase totals = $1,242.20       $1,366.6076   $1,366.60   $1,366.55   $1,366.60