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 $208.92   12.821%   $235.7056   $235.71   $235.70   $235.70  
  Purchase #2 $88.63   4.564%   $92.6751   $92.68   $92.70   $92.70  
  Purchase #3 $163.72   3.747%   $169.8546   $169.85   $169.85   $169.90  
  Purchase #4 $156.34   3.198%   $161.3398   $161.34   $161.35   $161.30  
  Purchase #5 $15.75   9.450%   $17.2384   $17.24   $17.25   $17.20  
  Purchase #6 $244.31   11.408%   $272.1809   $272.18   $272.20   $272.20  
  Purchase #7 $116.84   9.692%   $128.1641   $128.16   $128.15   $128.20  
  7 purchase totals = $994.51       $1,077.1585   $1,077.16   $1,077.20   $1,077.20