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 $88.50   12.206%   $99.3023   $99.30   $99.30   $99.30  
  Purchase #2 $134.89   10.874%   $149.5579   $149.56   $149.55   $149.60  
  Purchase #3 $155.85   12.560%   $175.4248   $175.42   $175.40   $175.40  
  Purchase #4 $175.81   12.627%   $198.0095   $198.01   $198.00   $198.00  
  Purchase #5 $48.61   6.493%   $51.7662   $51.77   $51.75   $51.80  
  Purchase #6 $205.57   5.123%   $216.1014   $216.10   $216.10   $216.10  
  Purchase #7 $187.72   12.372%   $210.9447   $210.94   $210.95   $210.90  
  7 purchase totals = $996.95       $1,101.1068   $1,101.10   $1,101.05   $1,101.10