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 $55.28   6.809%   $59.044   $59.04   $59.05   $59.00  
  Purchase #2 $84.35   4.548%   $88.1862   $88.19   $88.20   $88.20  
  Purchase #3 $51.59   10.158%   $56.8305   $56.83   $56.85   $56.80  
  Purchase #4 $166.39   8.602%   $180.7029   $180.70   $180.70   $180.70  
  Purchase #5 $68.98   7.343%   $74.0452   $74.05   $74.05   $74.00  
  Purchase #6 $177.25   8.419%   $192.1727   $192.17   $192.15   $192.20  
  Purchase #7 $101.80   7.458%   $109.3922   $109.39   $109.40   $109.40  
  7 purchase totals = $705.64       $760.3737   $760.37   $760.40   $760.30