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 $197.50   5.287%   $207.9418   $207.94   $207.95   $207.90  
  Purchase #2 $175.67   10.760%   $194.5721   $194.57   $194.55   $194.60  
  Purchase #3 $68.79   8.671%   $74.7548   $74.75   $74.75   $74.80  
  Purchase #4 $114.31   7.701%   $123.113   $123.11   $123.10   $123.10  
  Purchase #5 $128.72   4.575%   $134.6089   $134.61   $134.60   $134.60  
  Purchase #6 $34.73   3.709%   $36.0181   $36.02   $36.00   $36.00  
  Purchase #7 $246.80   5.507%   $260.3913   $260.39   $260.40   $260.40  
  7 purchase totals = $966.52       $1,031.4000   $1,031.39   $1,031.35   $1,031.40