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 $62.67   11.763%   $70.0419   $70.04   $70.05   $70.00  
  Purchase #2 $235.95   7.141%   $252.7992   $252.80   $252.80   $252.80  
  Purchase #3 $18.67   4.707%   $19.5488   $19.55   $19.55   $19.50  
  Purchase #4 $192.52   5.657%   $203.4109   $203.41   $203.40   $203.40  
  Purchase #5 $190.46   5.121%   $200.2135   $200.21   $200.20   $200.20  
  Purchase #6 $12.49   10.403%   $13.7893   $13.79   $13.80   $13.80  
  Purchase #7 $6.35   6.241%   $6.7463   $6.75   $6.75   $6.70  
  7 purchase totals = $719.11       $766.5499   $766.55   $766.55   $766.40