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 $26.65   3.262%   $27.5193   $27.52   $27.50   $27.50  
  Purchase #2 $73.26   12.394%   $82.3398   $82.34   $82.35   $82.30  
  Purchase #3 $112.81   5.113%   $118.578   $118.58   $118.60   $118.60  
  Purchase #4 $41.50   8.446%   $45.0051   $45.01   $45.00   $45.00  
  Purchase #5 $177.29   7.787%   $191.0956   $191.10   $191.10   $191.10  
  Purchase #6 $223.87   12.207%   $251.1978   $251.20   $251.20   $251.20  
  Purchase #7 $7.88   4.778%   $8.2565   $8.26   $8.25   $8.30  
  7 purchase totals = $663.26       $723.9921   $724.01   $724.00   $724.00