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 $114.39   6.792%   $122.1594   $122.16   $122.15   $122.20  
  Purchase #2 $175.92   12.417%   $197.764   $197.76   $197.75   $197.80  
  Purchase #3 $35.30   10.808%   $39.1152   $39.12   $39.10   $39.10  
  Purchase #4 $82.50   11.229%   $91.7639   $91.76   $91.75   $91.80  
  Purchase #5 $159.77   9.780%   $175.3955   $175.40   $175.40   $175.40  
  Purchase #6 $166.66   4.247%   $173.7381   $173.74   $173.75   $173.70  
  Purchase #7 $228.56   11.137%   $254.0147   $254.01   $254.00   $254.00  
  7 purchase totals = $963.10       $1,053.9508   $1,053.95   $1,053.90   $1,054.00