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 $191.62   6.768%   $204.5888   $204.59   $204.60   $204.60  
  Purchase #2 $145.83   11.216%   $162.1863   $162.19   $162.20   $162.20  
  Purchase #3 $22.37   8.102%   $24.1824   $24.18   $24.20   $24.20  
  Purchase #4 $117.55   9.728%   $128.9853   $128.99   $129.00   $129.00  
  Purchase #5 $229.57   13.558%   $260.6951   $260.70   $260.70   $260.70  
  Purchase #6 $52.93   12.796%   $59.7029   $59.70   $59.70   $59.70  
  Purchase #7 $151.37   6.287%   $160.8866   $160.89   $160.90   $160.90  
  7 purchase totals = $911.24       $1,001.2274   $1,001.24   $1,001.30   $1,001.30