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 $184.61   12.479%   $207.6475   $207.65   $207.65   $207.60  
  Purchase #2 $95.31   9.133%   $104.0147   $104.01   $104.00   $104.00  
  Purchase #3 $250.52   12.688%   $282.306   $282.31   $282.30   $282.30  
  Purchase #4 $93.78   10.725%   $103.8379   $103.84   $103.85   $103.80  
  Purchase #5 $140.78   3.791%   $146.117   $146.12   $146.10   $146.10  
  Purchase #6 $197.88   10.776%   $219.2035   $219.20   $219.20   $219.20  
  Purchase #7 $114.88   5.458%   $121.1502   $121.15   $121.15   $121.20  
  7 purchase totals = $1,077.76       $1,184.2768   $1,184.28   $1,184.25   $1,184.20