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 $194.30   13.182%   $219.9126   $219.91   $219.90   $219.90  
  Purchase #2 $59.34   4.856%   $62.2216   $62.22   $62.20   $62.20  
  Purchase #3 $103.57   11.646%   $115.6318   $115.63   $115.65   $115.60  
  Purchase #4 $71.89   3.605%   $74.4816   $74.48   $74.50   $74.50  
  Purchase #5 $144.96   3.334%   $149.793   $149.79   $149.80   $149.80  
  Purchase #6 $128.52   4.487%   $134.2867   $134.29   $134.30   $134.30  
  Purchase #7 $245.41   7.157%   $262.974   $262.97   $262.95   $263.00  
  7 purchase totals = $947.99       $1,019.3013   $1,019.29   $1,019.30   $1,019.30