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 $45.97   5.253%   $48.3848   $48.38   $48.40   $48.40  
  Purchase #2 $237.92   9.232%   $259.8848   $259.88   $259.90   $259.90  
  Purchase #3 $220.49   11.279%   $245.3591   $245.36   $245.35   $245.40  
  Purchase #4 $246.60   9.568%   $270.1947   $270.19   $270.20   $270.20  
  Purchase #5 $166.42   6.707%   $177.5818   $177.58   $177.60   $177.60  
  Purchase #6 $41.50   11.454%   $46.2534   $46.25   $46.25   $46.30  
  Purchase #7 $8.60   12.688%   $9.6912   $9.69   $9.70   $9.70  
  7 purchase totals = $967.50       $1,057.3498   $1,057.33   $1,057.40   $1,057.50