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 $113.68   7.356%   $122.0423   $122.04   $122.05   $122.00  
  Purchase #2 $146.75   13.556%   $166.6434   $166.64   $166.65   $166.60  
  Purchase #3 $169.48   10.370%   $187.0551   $187.06   $187.05   $187.10  
  Purchase #4 $148.61   12.617%   $167.3601   $167.36   $167.35   $167.40  
  Purchase #5 $184.99   8.221%   $200.198   $200.20   $200.20   $200.20  
  Purchase #6 $14.91   6.135%   $15.8247   $15.82   $15.80   $15.80  
  Purchase #7 $201.82   10.696%   $223.4067   $223.41   $223.40   $223.40  
  7 purchase totals = $980.24       $1,082.5303   $1,082.53   $1,082.50   $1,082.50