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 $189.61   5.111%   $199.301   $199.30   $199.30   $199.30  
  Purchase #2 $205.94   5.809%   $217.9031   $217.90   $217.90   $217.90  
  Purchase #3 $215.68   13.495%   $244.786   $244.79   $244.80   $244.80  
  Purchase #4 $68.54   7.281%   $73.5304   $73.53   $73.55   $73.50  
  Purchase #5 $212.74   7.644%   $229.0018   $229.00   $229.00   $229.00  
  Purchase #6 $101.92   12.459%   $114.6182   $114.62   $114.60   $114.60  
  Purchase #7 $29.35   7.826%   $31.6469   $31.65   $31.65   $31.60  
  7 purchase totals = $1,023.78       $1,110.7874   $1,110.79   $1,110.80   $1,110.70