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 $213.70   10.209%   $235.5166   $235.52   $235.50   $235.50  
  Purchase #2 $95.41   11.311%   $106.2018   $106.20   $106.20   $106.20  
  Purchase #3 $186.73   13.503%   $211.9442   $211.94   $211.95   $211.90  
  Purchase #4 $120.32   10.672%   $133.1606   $133.16   $133.15   $133.20  
  Purchase #5 $7.56   13.229%   $8.5601   $8.56   $8.55   $8.60  
  Purchase #6 $245.68   9.491%   $268.9975   $269.00   $269.00   $269.00  
  Purchase #7 $87.42   7.573%   $94.0403   $94.04   $94.05   $94.00  
  7 purchase totals = $956.82       $1,058.4211   $1,058.42   $1,058.40   $1,058.40