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 $61.77   9.545%   $67.6659   $67.67   $67.65   $67.70  
  Purchase #2 $231.53   11.221%   $257.51   $257.51   $257.50   $257.50  
  Purchase #3 $176.46   12.245%   $198.0675   $198.07   $198.05   $198.10  
  Purchase #4 $36.79   6.220%   $39.0783   $39.08   $39.10   $39.10  
  Purchase #5 $197.43   9.703%   $216.5866   $216.59   $216.60   $216.60  
  Purchase #6 $87.73   11.582%   $97.8909   $97.89   $97.90   $97.90  
  Purchase #7 $25.32   4.848%   $26.5475   $26.55   $26.55   $26.50  
  7 purchase totals = $817.03       $903.3467   $903.36   $903.35   $903.40