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 $182.34   12.195%   $204.5764   $204.58   $204.60   $204.60  
  Purchase #2 $198.97   4.774%   $208.4688   $208.47   $208.45   $208.50  
  Purchase #3 $134.88   11.845%   $150.8565   $150.86   $150.85   $150.90  
  Purchase #4 $203.74   9.816%   $223.7391   $223.74   $223.75   $223.70  
  Purchase #5 $40.77   12.731%   $45.9604   $45.96   $45.95   $46.00  
  Purchase #6 $37.83   5.316%   $39.841   $39.84   $39.85   $39.80  
  Purchase #7 $186.80   4.559%   $195.3162   $195.32   $195.30   $195.30  
  7 purchase totals = $985.33       $1,068.7584   $1,068.77   $1,068.75   $1,068.80