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 $180.96   8.831%   $196.9406   $196.94   $196.95   $196.90  
  Purchase #2 $149.41   7.593%   $160.7547   $160.75   $160.75   $160.80  
  Purchase #3 $84.90   6.325%   $90.2699   $90.27   $90.25   $90.30  
  Purchase #4 $220.95   9.207%   $241.2929   $241.29   $241.30   $241.30  
  Purchase #5 $129.58   5.221%   $136.3454   $136.35   $136.35   $136.30  
  Purchase #6 $216.46   7.158%   $231.9542   $231.95   $231.95   $232.00  
  Purchase #7 $177.95   13.145%   $201.3415   $201.34   $201.35   $201.30  
  7 purchase totals = $1,160.21       $1,258.8992   $1,258.89   $1,258.90   $1,258.90