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 $148.43   12.519%   $167.012   $167.01   $167.00   $167.00  
  Purchase #2 $186.80   6.190%   $198.3629   $198.36   $198.35   $198.40  
  Purchase #3 $65.88   8.464%   $71.4561   $71.46   $71.45   $71.50  
  Purchase #4 $240.75   7.701%   $259.2902   $259.29   $259.30   $259.30  
  Purchase #5 $64.71   13.396%   $73.3786   $73.38   $73.40   $73.40  
  Purchase #6 $39.59   8.868%   $43.1008   $43.10   $43.10   $43.10  
  Purchase #7 $215.78   11.336%   $240.2408   $240.24   $240.25   $240.20  
  7 purchase totals = $961.94       $1,052.8414   $1,052.84   $1,052.85   $1,052.90