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 $220.94   10.671%   $244.5165   $244.52   $244.50   $244.50  
  Purchase #2 $26.74   9.791%   $29.3581   $29.36   $29.35   $29.40  
  Purchase #3 $226.30   8.784%   $246.1782   $246.18   $246.20   $246.20  
  Purchase #4 $184.44   13.201%   $208.7879   $208.79   $208.80   $208.80  
  Purchase #5 $169.32   5.356%   $178.3888   $178.39   $178.40   $178.40  
  Purchase #6 $22.63   7.831%   $24.4022   $24.40   $24.40   $24.40  
  Purchase #7 $124.75   3.219%   $128.7657   $128.77   $128.75   $128.80  
  7 purchase totals = $975.12       $1,060.3974   $1,060.41   $1,060.40   $1,060.50