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 $67.96   10.422%   $75.0428   $75.04   $75.05   $75.00  
  Purchase #2 $215.40   6.205%   $228.7656   $228.77   $228.75   $228.80  
  Purchase #3 $229.52   10.604%   $253.8583   $253.86   $253.85   $253.90  
  Purchase #4 $45.31   4.796%   $47.4831   $47.48   $47.50   $47.50  
  Purchase #5 $215.65   3.543%   $223.2905   $223.29   $223.30   $223.30  
  Purchase #6 $114.56   10.516%   $126.6071   $126.61   $126.60   $126.60  
  Purchase #7 $168.36   10.483%   $186.0092   $186.01   $186.00   $186.00  
  7 purchase totals = $1,056.76       $1,141.0566   $1,141.06   $1,141.05   $1,141.10