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 $188.68   12.247%   $211.7876   $211.79   $211.80   $211.80  
  Purchase #2 $96.73   5.489%   $102.0395   $102.04   $102.05   $102.00  
  Purchase #3 $112.40   12.595%   $126.5568   $126.56   $126.55   $126.60  
  Purchase #4 $197.51   13.152%   $223.4865   $223.49   $223.50   $223.50  
  Purchase #5 $198.94   8.231%   $215.3148   $215.31   $215.30   $215.30  
  Purchase #6 $58.77   11.765%   $65.6843   $65.68   $65.70   $65.70  
  Purchase #7 $85.67   3.505%   $88.6727   $88.67   $88.65   $88.70  
  7 purchase totals = $938.70       $1,033.5422   $1,033.54   $1,033.55   $1,033.60