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 $146.75   9.719%   $161.0126   $161.01   $161.00   $161.00  
  Purchase #2 $208.82   13.454%   $236.9146   $236.91   $236.90   $236.90  
  Purchase #3 $223.77   12.132%   $250.9178   $250.92   $250.90   $250.90  
  Purchase #4 $108.29   4.705%   $113.385   $113.39   $113.40   $113.40  
  Purchase #5 $149.94   8.607%   $162.8453   $162.85   $162.85   $162.80  
  Purchase #6 $55.82   13.221%   $63.2   $63.20   $63.20   $63.20  
  Purchase #7 $88.61   6.227%   $94.1277   $94.13   $94.15   $94.10  
  7 purchase totals = $982.00       $1,082.4030   $1,082.41   $1,082.40   $1,082.30