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 $194.69   5.596%   $205.5849   $205.58   $205.60   $205.60  
  Purchase #2 $48.77   6.619%   $51.9981   $52.00   $52.00   $52.00  
  Purchase #3 $47.29   13.457%   $53.6538   $53.65   $53.65   $53.70  
  Purchase #4 $227.43   3.182%   $234.6668   $234.67   $234.65   $234.70  
  Purchase #5 $244.93   9.392%   $267.9338   $267.93   $267.95   $267.90  
  Purchase #6 $19.83   5.870%   $20.994   $20.99   $21.00   $21.00  
  Purchase #7 $166.28   11.415%   $185.2609   $185.26   $185.25   $185.30  
  7 purchase totals = $949.22       $1,020.0923   $1,020.08   $1,020.10   $1,020.20