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 $211.58   5.762%   $223.7712   $223.77   $223.75   $223.80  
  Purchase #2 $130.72   12.721%   $147.3489   $147.35   $147.35   $147.30  
  Purchase #3 $143.40   7.487%   $154.1364   $154.14   $154.15   $154.10  
  Purchase #4 $214.96   10.236%   $236.9633   $236.96   $236.95   $237.00  
  Purchase #5 $42.66   5.438%   $44.9799   $44.98   $45.00   $45.00  
  Purchase #6 $116.42   10.281%   $128.3891   $128.39   $128.40   $128.40  
  Purchase #7 $78.90   11.545%   $88.009   $88.01   $88.00   $88.00  
  7 purchase totals = $938.64       $1,023.5978   $1,023.60   $1,023.60   $1,023.60