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 $87.31   7.611%   $93.9552   $93.96   $93.95   $94.00  
  Purchase #2 $242.48   11.804%   $271.1023   $271.10   $271.10   $271.10  
  Purchase #3 $246.91   7.673%   $265.8554   $265.86   $265.85   $265.90  
  Purchase #4 $204.40   10.215%   $225.2795   $225.28   $225.30   $225.30  
  Purchase #5 $128.28   9.769%   $140.8117   $140.81   $140.80   $140.80  
  Purchase #6 $130.99   4.318%   $136.6461   $136.65   $136.65   $136.60  
  Purchase #7 $212.50   5.403%   $223.9814   $223.98   $224.00   $224.00  
  7 purchase totals = $1,252.87       $1,357.6316   $1,357.64   $1,357.65   $1,357.70