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 $247.83   9.619%   $271.6688   $271.67   $271.65   $271.70  
  Purchase #2 $215.52   12.263%   $241.9492   $241.95   $241.95   $241.90  
  Purchase #3 $84.59   4.711%   $88.575   $88.58   $88.60   $88.60  
  Purchase #4 $245.35   12.398%   $275.7685   $275.77   $275.75   $275.80  
  Purchase #5 $247.33   9.497%   $270.8189   $270.82   $270.80   $270.80  
  Purchase #6 $137.75   8.491%   $149.4464   $149.45   $149.45   $149.40  
  Purchase #7 $163.55   10.675%   $181.009   $181.01   $181.00   $181.00  
  7 purchase totals = $1,341.92       $1,479.2358   $1,479.25   $1,479.20   $1,479.20