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 $161.96   8.409%   $175.5792   $175.58   $175.60   $175.60  
  Purchase #2 $52.37   12.676%   $59.0084   $59.01   $59.00   $59.00  
  Purchase #3 $187.35   3.852%   $194.5667   $194.57   $194.55   $194.60  
  Purchase #4 $63.25   5.813%   $66.9267   $66.93   $66.95   $66.90  
  Purchase #5 $178.75   12.861%   $201.739   $201.74   $201.75   $201.70  
  Purchase #6 $241.58   12.452%   $271.6615   $271.66   $271.65   $271.70  
  Purchase #7 $195.88   10.862%   $217.1565   $217.16   $217.15   $217.20  
  7 purchase totals = $1,081.14       $1,186.6380   $1,186.65   $1,186.65   $1,186.70