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 $66.52   11.186%   $73.9609   $73.96   $73.95   $74.00  
  Purchase #2 $52.49   13.751%   $59.7079   $59.71   $59.70   $59.70  
  Purchase #3 $163.39   8.297%   $176.9465   $176.95   $176.95   $176.90  
  Purchase #4 $23.25   3.733%   $24.1179   $24.12   $24.10   $24.10  
  Purchase #5 $56.70   3.793%   $58.8506   $58.85   $58.85   $58.90  
  Purchase #6 $163.49   9.327%   $178.7387   $178.74   $178.75   $178.70  
  Purchase #7 $245.35   4.122%   $255.4633   $255.46   $255.45   $255.50  
  7 purchase totals = $771.19       $827.7858   $827.79   $827.75   $827.80