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 $141.52   10.753%   $156.7376   $156.74   $156.75   $156.70  
  Purchase #2 $65.90   5.694%   $69.6523   $69.65   $69.65   $69.70  
  Purchase #3 $246.88   9.475%   $270.2719   $270.27   $270.25   $270.30  
  Purchase #4 $58.37   7.559%   $62.7822   $62.78   $62.80   $62.80  
  Purchase #5 $203.52   12.201%   $228.3515   $228.35   $228.35   $228.40  
  Purchase #6 $249.39   13.156%   $282.1997   $282.20   $282.20   $282.20  
  Purchase #7 $9.63   3.145%   $9.9329   $9.93   $9.95   $9.90  
  7 purchase totals = $975.21       $1,079.9281   $1,079.92   $1,079.95   $1,080.00