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 $246.61   7.697%   $265.5916   $265.59   $265.60   $265.60  
  Purchase #2 $147.90   5.682%   $156.3037   $156.30   $156.30   $156.30  
  Purchase #3 $80.77   9.434%   $88.3898   $88.39   $88.40   $88.40  
  Purchase #4 $109.67   10.393%   $121.068   $121.07   $121.05   $121.10  
  Purchase #5 $152.47   8.825%   $165.9255   $165.93   $165.95   $165.90  
  Purchase #6 $217.60   8.459%   $236.0068   $236.01   $236.00   $236.00  
  Purchase #7 $43.47   13.362%   $49.2785   $49.28   $49.30   $49.30  
  7 purchase totals = $998.49       $1,082.5639   $1,082.57   $1,082.60   $1,082.60