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 $66.93   7.591%   $72.0107   $72.01   $72.00   $72.00  
  Purchase #2 $154.79   8.473%   $167.9054   $167.91   $167.90   $167.90  
  Purchase #3 $246.96   11.498%   $275.3555   $275.36   $275.35   $275.40  
  Purchase #4 $73.66   9.747%   $80.8396   $80.84   $80.85   $80.80  
  Purchase #5 $220.28   13.235%   $249.4341   $249.43   $249.45   $249.40  
  Purchase #6 $123.37   7.597%   $132.7424   $132.74   $132.75   $132.70  
  Purchase #7 $100.88   13.494%   $114.4927   $114.49   $114.50   $114.50  
  7 purchase totals = $986.87       $1,092.7804   $1,092.78   $1,092.80   $1,092.70