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 $211.75   6.269%   $225.0246   $225.02   $225.00   $225.00  
  Purchase #2 $102.96   13.632%   $116.9955   $117.00   $117.00   $117.00  
  Purchase #3 $93.70   10.311%   $103.3614   $103.36   $103.35   $103.40  
  Purchase #4 $238.97   6.106%   $253.5615   $253.56   $253.55   $253.60  
  Purchase #5 $72.39   10.751%   $80.1726   $80.17   $80.15   $80.20  
  Purchase #6 $53.51   10.344%   $59.0451   $59.05   $59.05   $59.00  
  Purchase #7 $185.53   6.511%   $197.6099   $197.61   $197.60   $197.60  
  7 purchase totals = $958.81       $1,035.7706   $1,035.77   $1,035.70   $1,035.80