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 $159.39   4.750%   $166.961   $166.96   $166.95   $167.00  
  Purchase #2 $194.55   11.357%   $216.645   $216.65   $216.65   $216.60  
  Purchase #3 $234.74   12.645%   $264.4229   $264.42   $264.40   $264.40  
  Purchase #4 $95.73   4.226%   $99.7755   $99.78   $99.80   $99.80  
  Purchase #5 $188.65   4.413%   $196.9751   $196.98   $197.00   $197.00  
  Purchase #6 $67.55   9.171%   $73.745   $73.75   $73.75   $73.70  
  Purchase #7 $84.85   12.699%   $95.6251   $95.63   $95.65   $95.60  
  7 purchase totals = $1,025.46       $1,114.1496   $1,114.17   $1,114.20   $1,114.10