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 $60.90   13.359%   $69.0356   $69.04   $69.05   $69.00  
  Purchase #2 $87.93   12.134%   $98.5994   $98.60   $98.60   $98.60  
  Purchase #3 $151.37   3.204%   $156.2199   $156.22   $156.20   $156.20  
  Purchase #4 $226.67   7.717%   $244.1621   $244.16   $244.15   $244.20  
  Purchase #5 $215.78   12.709%   $243.2035   $243.20   $243.20   $243.20  
  Purchase #6 $31.83   5.656%   $33.6303   $33.63   $33.65   $33.60  
  Purchase #7 $219.70   3.157%   $226.6359   $226.64   $226.65   $226.60  
  7 purchase totals = $994.18       $1,071.4867   $1,071.49   $1,071.50   $1,071.40