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 $66.56   4.754%   $69.7243   $69.72   $69.70   $69.70  
  Purchase #2 $159.41   9.563%   $174.6544   $174.65   $174.65   $174.70  
  Purchase #3 $175.83   5.171%   $184.9222   $184.92   $184.90   $184.90  
  Purchase #4 $202.42   7.160%   $216.9133   $216.91   $216.90   $216.90  
  Purchase #5 $183.52   4.277%   $191.3692   $191.37   $191.35   $191.40  
  Purchase #6 $5.50   8.363%   $5.96   $5.96   $5.95   $6.00  
  Purchase #7 $191.76   3.871%   $199.183   $199.18   $199.20   $199.20  
  7 purchase totals = $985.00       $1,042.7264   $1,042.71   $1,042.65   $1,042.80