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 $65.81   11.385%   $73.3025   $73.30   $73.30   $73.30  
  Purchase #2 $16.27   6.326%   $17.2992   $17.30   $17.30   $17.30  
  Purchase #3 $30.71   5.132%   $32.286   $32.29   $32.30   $32.30  
  Purchase #4 $84.45   5.120%   $88.7738   $88.77   $88.75   $88.80  
  Purchase #5 $166.52   10.555%   $184.0962   $184.10   $184.10   $184.10  
  Purchase #6 $229.76   11.530%   $256.2513   $256.25   $256.25   $256.30  
  Purchase #7 $102.59   5.841%   $108.5823   $108.58   $108.60   $108.60  
  7 purchase totals = $696.11       $760.5913   $760.59   $760.60   $760.70