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 $218.49   11.669%   $243.9856   $243.99   $244.00   $244.00  
  Purchase #2 $65.79   12.418%   $73.9598   $73.96   $73.95   $74.00  
  Purchase #3 $207.81   8.228%   $224.9086   $224.91   $224.90   $224.90  
  Purchase #4 $212.85   12.213%   $238.8454   $238.85   $238.85   $238.80  
  Purchase #5 $20.52   5.107%   $21.568   $21.57   $21.55   $21.60  
  Purchase #6 $73.71   11.470%   $82.1645   $82.16   $82.15   $82.20  
  Purchase #7 $26.94   7.204%   $28.8808   $28.88   $28.90   $28.90  
  7 purchase totals = $826.11       $914.3127   $914.32   $914.30   $914.40