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 $119.81   9.841%   $131.6005   $131.60   $131.60   $131.60  
  Purchase #2 $14.92   7.357%   $16.0177   $16.02   $16.00   $16.00  
  Purchase #3 $203.64   4.316%   $212.4291   $212.43   $212.45   $212.40  
  Purchase #4 $115.53   3.450%   $119.5158   $119.52   $119.50   $119.50  
  Purchase #5 $207.27   10.152%   $228.3121   $228.31   $228.30   $228.30  
  Purchase #6 $93.87   8.786%   $102.1174   $102.12   $102.10   $102.10  
  Purchase #7 $212.66   6.164%   $225.7684   $225.77   $225.75   $225.80  
  7 purchase totals = $967.70       $1,035.7610   $1,035.77   $1,035.70   $1,035.70