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 $187.34   6.233%   $199.0169   $199.02   $199.00   $199.00  
  Purchase #2 $216.46   8.732%   $235.3613   $235.36   $235.35   $235.40  
  Purchase #3 $216.25   6.237%   $229.7375   $229.74   $229.75   $229.70  
  Purchase #4 $196.69   12.219%   $220.7236   $220.72   $220.70   $220.70  
  Purchase #5 $68.36   7.422%   $73.4337   $73.43   $73.45   $73.40  
  Purchase #6 $52.53   5.673%   $55.51   $55.51   $55.50   $55.50  
  Purchase #7 $18.94   12.734%   $21.3518   $21.35   $21.35   $21.40  
  7 purchase totals = $956.57       $1,035.1348   $1,035.13   $1,035.10   $1,035.10