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 $83.84   5.811%   $88.7119   $88.71   $88.70   $88.70  
  Purchase #2 $218.34   10.857%   $242.0452   $242.05   $242.05   $242.00  
  Purchase #3 $82.97   7.613%   $89.2865   $89.29   $89.30   $89.30  
  Purchase #4 $162.77   5.649%   $171.9649   $171.96   $171.95   $172.00  
  Purchase #5 $153.99   4.360%   $160.704   $160.70   $160.70   $160.70  
  Purchase #6 $200.72   7.293%   $215.3585   $215.36   $215.35   $215.40  
  Purchase #7 $68.55   8.272%   $74.2205   $74.22   $74.20   $74.20  
  7 purchase totals = $971.18       $1,042.2915   $1,042.29   $1,042.25   $1,042.30