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 $64.51   3.251%   $66.6072   $66.61   $66.60   $66.60  
  Purchase #2 $152.98   4.577%   $159.9819   $159.98   $160.00   $160.00  
  Purchase #3 $24.52   3.185%   $25.301   $25.30   $25.30   $25.30  
  Purchase #4 $12.61   8.232%   $13.6481   $13.65   $13.65   $13.60  
  Purchase #5 $217.99   3.158%   $224.8741   $224.87   $224.85   $224.90  
  Purchase #6 $141.41   5.620%   $149.3572   $149.36   $149.35   $149.40  
  Purchase #7 $106.68   4.806%   $111.807   $111.81   $111.80   $111.80  
  7 purchase totals = $720.70       $751.5765   $751.58   $751.55   $751.60