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 $38.92   13.746%   $44.2699   $44.27   $44.25   $44.30  
  Purchase #2 $193.97   9.829%   $213.0353   $213.04   $213.05   $213.00  
  Purchase #3 $202.43   8.340%   $219.3127   $219.31   $219.30   $219.30  
  Purchase #4 $157.50   11.542%   $175.6787   $175.68   $175.70   $175.70  
  Purchase #5 $154.73   3.299%   $159.8345   $159.83   $159.85   $159.80  
  Purchase #6 $75.36   6.823%   $80.5018   $80.50   $80.50   $80.50  
  Purchase #7 $203.37   8.557%   $220.7724   $220.77   $220.75   $220.80  
  7 purchase totals = $1,026.28       $1,113.4053   $1,113.40   $1,113.40   $1,113.40