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 $188.96   8.347%   $204.7325   $204.73   $204.75   $204.70  
  Purchase #2 $8.70   12.546%   $9.7915   $9.79   $9.80   $9.80  
  Purchase #3 $163.77   13.126%   $185.2665   $185.27   $185.25   $185.30  
  Purchase #4 $181.79   3.403%   $187.9763   $187.98   $188.00   $188.00  
  Purchase #5 $95.43   12.771%   $107.6174   $107.62   $107.60   $107.60  
  Purchase #6 $186.37   5.183%   $196.0296   $196.03   $196.05   $196.00  
  Purchase #7 $145.55   4.355%   $151.8887   $151.89   $151.90   $151.90  
  7 purchase totals = $970.57       $1,043.3025   $1,043.31   $1,043.35   $1,043.30