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 $53.74   11.219%   $59.7691   $59.77   $59.75   $59.80  
  Purchase #2 $101.37   3.406%   $104.8227   $104.82   $104.80   $104.80  
  Purchase #3 $196.46   13.854%   $223.6776   $223.68   $223.70   $223.70  
  Purchase #4 $181.31   11.142%   $201.5116   $201.51   $201.50   $201.50  
  Purchase #5 $141.84   11.487%   $158.1332   $158.13   $158.15   $158.10  
  Purchase #6 $248.51   8.709%   $270.1527   $270.15   $270.15   $270.20  
  Purchase #7 $5.60   12.562%   $6.3035   $6.30   $6.30   $6.30  
  7 purchase totals = $928.83       $1,024.3704   $1,024.36   $1,024.35   $1,024.40