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 $186.26   6.140%   $197.6964   $197.70   $197.70   $197.70  
  Purchase #2 $91.93   11.832%   $102.8072   $102.81   $102.80   $102.80  
  Purchase #3 $68.26   4.557%   $71.3706   $71.37   $71.35   $71.40  
  Purchase #4 $105.37   6.674%   $112.4024   $112.40   $112.40   $112.40  
  Purchase #5 $54.30   4.469%   $56.7267   $56.73   $56.75   $56.70  
  Purchase #6 $184.78   10.103%   $203.4483   $203.45   $203.45   $203.40  
  Purchase #7 $211.37   9.594%   $231.6488   $231.65   $231.65   $231.60  
  7 purchase totals = $902.27       $976.1004   $976.11   $976.10   $976.00