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 $241.27   9.380%   $263.9011   $263.90   $263.90   $263.90  
  Purchase #2 $29.50   4.503%   $30.8284   $30.83   $30.85   $30.80  
  Purchase #3 $31.39   13.146%   $35.5165   $35.52   $35.50   $35.50  
  Purchase #4 $240.98   8.700%   $261.9453   $261.95   $261.95   $261.90  
  Purchase #5 $204.29   9.552%   $223.8038   $223.80   $223.80   $223.80  
  Purchase #6 $36.26   8.517%   $39.3483   $39.35   $39.35   $39.30  
  Purchase #7 $190.80   4.566%   $199.5119   $199.51   $199.50   $199.50  
  7 purchase totals = $974.49       $1,054.8553   $1,054.86   $1,054.85   $1,054.70