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 $236.58   10.115%   $260.5101   $260.51   $260.50   $260.50  
  Purchase #2 $214.88   6.352%   $228.5292   $228.53   $228.55   $228.50  
  Purchase #3 $85.42   7.593%   $91.9059   $91.91   $91.90   $91.90  
  Purchase #4 $223.29   11.314%   $248.553   $248.55   $248.55   $248.60  
  Purchase #5 $128.35   13.133%   $145.2062   $145.21   $145.20   $145.20  
  Purchase #6 $99.61   3.506%   $103.1023   $103.10   $103.10   $103.10  
  Purchase #7 $25.66   6.372%   $27.2951   $27.30   $27.30   $27.30  
  7 purchase totals = $1,013.79       $1,105.1018   $1,105.11   $1,105.10   $1,105.10