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 $236.51   12.109%   $265.149   $265.15   $265.15   $265.10  
  Purchase #2 $26.95   9.732%   $29.5728   $29.57   $29.55   $29.60  
  Purchase #3 $246.95   11.672%   $275.774   $275.77   $275.75   $275.80  
  Purchase #4 $203.29   13.466%   $230.665   $230.67   $230.65   $230.70  
  Purchase #5 $230.40   10.363%   $254.2764   $254.28   $254.30   $254.30  
  Purchase #6 $56.36   7.790%   $60.7504   $60.75   $60.75   $60.80  
  Purchase #7 $67.78   12.593%   $76.3155   $76.32   $76.30   $76.30  
  7 purchase totals = $1,068.24       $1,192.5031   $1,192.51   $1,192.45   $1,192.60