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 $166.62   6.429%   $177.332   $177.33   $177.35   $177.30  
  Purchase #2 $228.99   10.658%   $253.3958   $253.40   $253.40   $253.40  
  Purchase #3 $164.65   3.734%   $170.798   $170.80   $170.80   $170.80  
  Purchase #4 $232.42   4.694%   $243.3298   $243.33   $243.35   $243.30  
  Purchase #5 $5.35   3.534%   $5.5391   $5.54   $5.55   $5.50  
  Purchase #6 $80.99   4.828%   $84.9002   $84.90   $84.90   $84.90  
  Purchase #7 $155.71   4.761%   $163.1234   $163.12   $163.10   $163.10  
  7 purchase totals = $1,034.73       $1,098.4183   $1,098.42   $1,098.45   $1,098.30