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 $13.78   6.305%   $14.6488   $14.65   $14.65   $14.60  
  Purchase #2 $87.68   3.858%   $91.0627   $91.06   $91.05   $91.10  
  Purchase #3 $234.30   7.231%   $251.2422   $251.24   $251.25   $251.20  
  Purchase #4 $189.69   7.295%   $203.5279   $203.53   $203.55   $203.50  
  Purchase #5 $119.29   6.132%   $126.6049   $126.60   $126.60   $126.60  
  Purchase #6 $5.61   10.425%   $6.1948   $6.19   $6.20   $6.20  
  Purchase #7 $58.36   3.693%   $60.5152   $60.52   $60.50   $60.50  
  7 purchase totals = $708.71       $753.7965   $753.79   $753.80   $753.70