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 $221.94   13.230%   $251.3027   $251.30   $251.30   $251.30  
  Purchase #2 $220.71   5.278%   $232.3591   $232.36   $232.35   $232.40  
  Purchase #3 $95.57   13.111%   $108.1002   $108.10   $108.10   $108.10  
  Purchase #4 $243.73   9.655%   $267.2621   $267.26   $267.25   $267.30  
  Purchase #5 $24.89   3.398%   $25.7358   $25.74   $25.75   $25.70  
  Purchase #6 $92.69   4.343%   $96.7155   $96.72   $96.70   $96.70  
  Purchase #7 $130.59   3.487%   $135.1437   $135.14   $135.15   $135.10  
  7 purchase totals = $1,030.12       $1,116.6191   $1,116.62   $1,116.60   $1,116.60