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 $241.76   7.774%   $260.5544   $260.55   $260.55   $260.60  
  Purchase #2 $98.52   7.783%   $106.1878   $106.19   $106.20   $106.20  
  Purchase #3 $102.75   9.445%   $112.4547   $112.45   $112.45   $112.50  
  Purchase #4 $96.38   4.257%   $100.4829   $100.48   $100.50   $100.50  
  Purchase #5 $184.33   11.173%   $204.9252   $204.93   $204.95   $204.90  
  Purchase #6 $131.35   12.865%   $148.2482   $148.25   $148.25   $148.20  
  Purchase #7 $60.48   7.801%   $65.198   $65.20   $65.20   $65.20  
  7 purchase totals = $915.57       $998.0512   $998.05   $998.10   $998.10