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 $48.46   13.118%   $54.817   $54.82   $54.80   $54.80  
  Purchase #2 $220.87   5.245%   $232.4546   $232.45   $232.45   $232.50  
  Purchase #3 $66.31   10.821%   $73.4854   $73.49   $73.50   $73.50  
  Purchase #4 $248.35   11.123%   $275.974   $275.97   $275.95   $276.00  
  Purchase #5 $160.97   7.476%   $173.0041   $173.00   $173.00   $173.00  
  Purchase #6 $50.46   11.309%   $56.1665   $56.17   $56.15   $56.20  
  Purchase #7 $144.59   12.676%   $162.9182   $162.92   $162.90   $162.90  
  7 purchase totals = $940.01       $1,028.8198   $1,028.82   $1,028.75   $1,028.90