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 $60.76   4.259%   $63.3478   $63.35   $63.35   $63.30  
  Purchase #2 $188.87   7.471%   $202.9805   $202.98   $203.00   $203.00  
  Purchase #3 $145.52   9.716%   $159.6587   $159.66   $159.65   $159.70  
  Purchase #4 $60.27   8.691%   $65.5081   $65.51   $65.50   $65.50  
  Purchase #5 $73.41   11.130%   $81.5805   $81.58   $81.60   $81.60  
  Purchase #6 $236.85   7.483%   $254.5735   $254.57   $254.55   $254.60  
  Purchase #7 $116.89   6.365%   $124.33   $124.33   $124.35   $124.30  
  7 purchase totals = $882.57       $951.9791   $951.98   $952.00   $952.00