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 $198.26   3.594%   $205.3855   $205.39   $205.40   $205.40  
  Purchase #2 $58.57   3.415%   $60.5702   $60.57   $60.55   $60.60  
  Purchase #3 $60.28   8.196%   $65.2205   $65.22   $65.20   $65.20  
  Purchase #4 $90.50   3.182%   $93.3797   $93.38   $93.40   $93.40  
  Purchase #5 $232.49   3.791%   $241.3037   $241.30   $241.30   $241.30  
  Purchase #6 $231.84   5.213%   $243.9258   $243.93   $243.95   $243.90  
  Purchase #7 $226.46   11.273%   $251.9888   $251.99   $252.00   $252.00  
  7 purchase totals = $1,098.40       $1,161.7742   $1,161.78   $1,161.80   $1,161.80