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 $147.68   5.647%   $156.0195   $156.02   $156.00   $156.00  
  Purchase #2 $177.73   12.429%   $199.8201   $199.82   $199.80   $199.80  
  Purchase #3 $121.55   11.398%   $135.4043   $135.40   $135.40   $135.40  
  Purchase #4 $213.87   10.747%   $236.8546   $236.85   $236.85   $236.90  
  Purchase #5 $78.76   7.317%   $84.5229   $84.52   $84.50   $84.50  
  Purchase #6 $152.44   5.204%   $160.373   $160.37   $160.35   $160.40  
  Purchase #7 $69.34   5.146%   $72.9082   $72.91   $72.90   $72.90  
  7 purchase totals = $961.37       $1,045.9026   $1,045.89   $1,045.80   $1,045.90