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 $245.31   12.612%   $276.2485   $276.25   $276.25   $276.20  
  Purchase #2 $184.38   8.638%   $200.3067   $200.31   $200.30   $200.30  
  Purchase #3 $66.86   10.148%   $73.645   $73.65   $73.65   $73.60  
  Purchase #4 $176.74   7.394%   $189.8082   $189.81   $189.80   $189.80  
  Purchase #5 $143.55   6.518%   $152.9066   $152.91   $152.90   $152.90  
  Purchase #6 $247.75   6.647%   $264.2179   $264.22   $264.20   $264.20  
  Purchase #7 $200.25   8.470%   $217.2112   $217.21   $217.20   $217.20  
  7 purchase totals = $1,264.84       $1,374.3441   $1,374.36   $1,374.30   $1,374.20