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 $224.74   10.346%   $247.9916   $247.99   $248.00   $248.00  
  Purchase #2 $104.79   8.170%   $113.3513   $113.35   $113.35   $113.40  
  Purchase #3 $99.96   12.634%   $112.5889   $112.59   $112.60   $112.60  
  Purchase #4 $25.95   12.855%   $29.2859   $29.29   $29.30   $29.30  
  Purchase #5 $220.33   3.599%   $228.2597   $228.26   $228.25   $228.30  
  Purchase #6 $137.68   11.765%   $153.8781   $153.88   $153.90   $153.90  
  Purchase #7 $165.82   5.801%   $175.4392   $175.44   $175.45   $175.40  
  7 purchase totals = $979.27       $1,060.7947   $1,060.80   $1,060.85   $1,060.90