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 $97.73   12.184%   $109.6374   $109.64   $109.65   $109.60  
  Purchase #2 $215.95   11.651%   $241.1103   $241.11   $241.10   $241.10  
  Purchase #3 $18.99   3.216%   $19.6007   $19.60   $19.60   $19.60  
  Purchase #4 $189.82   11.659%   $211.9511   $211.95   $211.95   $212.00  
  Purchase #5 $96.86   13.860%   $110.2848   $110.28   $110.30   $110.30  
  Purchase #6 $19.56   11.535%   $21.8162   $21.82   $21.80   $21.80  
  Purchase #7 $196.65   7.495%   $211.3889   $211.39   $211.40   $211.40  
  7 purchase totals = $835.56       $925.7894   $925.79   $925.80   $925.80