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 $187.96   8.278%   $203.5193   $203.52   $203.50   $203.50  
  Purchase #2 $58.28   13.227%   $65.9887   $65.99   $66.00   $66.00  
  Purchase #3 $6.59   5.806%   $6.9726   $6.97   $6.95   $7.00  
  Purchase #4 $57.35   5.457%   $60.4796   $60.48   $60.50   $60.50  
  Purchase #5 $78.59   13.479%   $89.1831   $89.18   $89.20   $89.20  
  Purchase #6 $129.31   6.205%   $137.3337   $137.33   $137.35   $137.30  
  Purchase #7 $191.57   8.230%   $207.3362   $207.34   $207.35   $207.30  
  7 purchase totals = $709.65       $770.8132   $770.81   $770.85   $770.80