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 $180.67   8.474%   $195.98   $195.98   $196.00   $196.00  
  Purchase #2 $72.44   8.274%   $78.4337   $78.43   $78.45   $78.40  
  Purchase #3 $151.52   7.587%   $163.0158   $163.02   $163.00   $163.00  
  Purchase #4 $111.53   11.487%   $124.3415   $124.34   $124.35   $124.30  
  Purchase #5 $226.72   9.379%   $247.9841   $247.98   $248.00   $248.00  
  Purchase #6 $217.44   8.766%   $236.5008   $236.50   $236.50   $236.50  
  Purchase #7 $34.67   4.731%   $36.3102   $36.31   $36.30   $36.30  
  7 purchase totals = $994.99       $1,082.5661   $1,082.56   $1,082.60   $1,082.50