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 $235.51   11.783%   $263.2601   $263.26   $263.25   $263.30  
  Purchase #2 $33.89   8.144%   $36.65   $36.65   $36.65   $36.70  
  Purchase #3 $94.95   11.791%   $106.1456   $106.15   $106.15   $106.10  
  Purchase #4 $144.53   6.424%   $153.8146   $153.81   $153.80   $153.80  
  Purchase #5 $225.65   3.158%   $232.776   $232.78   $232.80   $232.80  
  Purchase #6 $54.41   12.658%   $61.2972   $61.30   $61.30   $61.30  
  Purchase #7 $157.67   4.283%   $164.423   $164.42   $164.40   $164.40  
  7 purchase totals = $946.61       $1,018.3665   $1,018.37   $1,018.35   $1,018.40