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 $57.85   11.777%   $64.663   $64.66   $64.65   $64.70  
  Purchase #2 $65.89   13.822%   $74.9973   $75.00   $75.00   $75.00  
  Purchase #3 $204.77   7.693%   $220.523   $220.52   $220.50   $220.50  
  Purchase #4 $183.61   5.123%   $193.0163   $193.02   $193.00   $193.00  
  Purchase #5 $50.83   10.439%   $56.1361   $56.14   $56.15   $56.10  
  Purchase #6 $187.65   3.403%   $194.0357   $194.04   $194.05   $194.00  
  Purchase #7 $187.62   6.499%   $199.8134   $199.81   $199.80   $199.80  
  7 purchase totals = $938.22       $1,003.1848   $1,003.19   $1,003.15   $1,003.10