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 $119.49   12.619%   $134.5684   $134.57   $134.55   $134.60  
  Purchase #2 $209.62   12.446%   $235.7093   $235.71   $235.70   $235.70  
  Purchase #3 $26.52   6.448%   $28.23   $28.23   $28.25   $28.20  
  Purchase #4 $241.31   6.519%   $257.041   $257.04   $257.05   $257.00  
  Purchase #5 $62.62   9.185%   $68.3716   $68.37   $68.35   $68.40  
  Purchase #6 $108.91   6.646%   $116.1482   $116.15   $116.15   $116.10  
  Purchase #7 $212.79   4.181%   $221.6867   $221.69   $221.70   $221.70  
  7 purchase totals = $981.26       $1,061.7552   $1,061.76   $1,061.75   $1,061.70