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 $47.39   7.706%   $51.0419   $51.04   $51.05   $51.00  
  Purchase #2 $138.52   12.380%   $155.6688   $155.67   $155.65   $155.70  
  Purchase #3 $219.69   12.118%   $246.312   $246.31   $246.30   $246.30  
  Purchase #4 $129.81   6.171%   $137.8206   $137.82   $137.80   $137.80  
  Purchase #5 $228.99   4.791%   $239.9609   $239.96   $239.95   $240.00  
  Purchase #6 $112.29   11.774%   $125.511   $125.51   $125.50   $125.50  
  Purchase #7 $163.29   10.346%   $180.184   $180.18   $180.20   $180.20  
  7 purchase totals = $1,039.98       $1,136.4992   $1,136.49   $1,136.45   $1,136.50