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 $134.81   8.565%   $146.3565   $146.36   $146.35   $146.40  
  Purchase #2 $100.98   6.517%   $107.5609   $107.56   $107.55   $107.60  
  Purchase #3 $202.72   10.858%   $224.7313   $224.73   $224.75   $224.70  
  Purchase #4 $139.97   9.863%   $153.7752   $153.78   $153.80   $153.80  
  Purchase #5 $159.84   9.372%   $174.8202   $174.82   $174.80   $174.80  
  Purchase #6 $234.25   10.575%   $259.0219   $259.02   $259.00   $259.00  
  Purchase #7 $8.41   13.341%   $9.532   $9.53   $9.55   $9.50  
  7 purchase totals = $980.98       $1,075.7980   $1,075.80   $1,075.80   $1,075.80