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 $24.53   9.415%   $26.8395   $26.84   $26.85   $26.80  
  Purchase #2 $160.78   12.747%   $181.2746   $181.27   $181.25   $181.30  
  Purchase #3 $223.97   5.152%   $235.5089   $235.51   $235.50   $235.50  
  Purchase #4 $161.76   5.870%   $171.2553   $171.26   $171.25   $171.30  
  Purchase #5 $84.56   8.260%   $91.5447   $91.54   $91.55   $91.50  
  Purchase #6 $110.51   5.659%   $116.7638   $116.76   $116.75   $116.80  
  Purchase #7 $228.98   6.521%   $243.9118   $243.91   $243.90   $243.90  
  7 purchase totals = $995.09       $1,067.0986   $1,067.09   $1,067.05   $1,067.10