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 $185.74   8.396%   $201.3347   $201.33   $201.35   $201.30  
  Purchase #2 $208.68   12.506%   $234.7775   $234.78   $234.80   $234.80  
  Purchase #3 $219.99   13.364%   $249.3895   $249.39   $249.40   $249.40  
  Purchase #4 $75.73   8.690%   $82.3109   $82.31   $82.30   $82.30  
  Purchase #5 $60.31   13.847%   $68.6611   $68.66   $68.65   $68.70  
  Purchase #6 $151.86   10.188%   $167.3315   $167.33   $167.35   $167.30  
  Purchase #7 $42.44   12.231%   $47.6308   $47.63   $47.65   $47.60  
  7 purchase totals = $944.75       $1,051.4360   $1,051.43   $1,051.50   $1,051.40