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 $32.52   6.397%   $34.6003   $34.60   $34.60   $34.60  
  Purchase #2 $197.52   11.604%   $220.4402   $220.44   $220.45   $220.40  
  Purchase #3 $60.56   12.220%   $67.9604   $67.96   $67.95   $68.00  
  Purchase #4 $51.26   10.701%   $56.7453   $56.75   $56.75   $56.70  
  Purchase #5 $147.34   3.595%   $152.6369   $152.64   $152.65   $152.60  
  Purchase #6 $82.27   11.633%   $91.8405   $91.84   $91.85   $91.80  
  Purchase #7 $223.93   4.518%   $234.0472   $234.05   $234.05   $234.00  
  7 purchase totals = $795.40       $858.2708   $858.28   $858.30   $858.10