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 $51.68   12.785%   $58.2873   $58.29   $58.30   $58.30  
  Purchase #2 $118.52   11.687%   $132.3714   $132.37   $132.35   $132.40  
  Purchase #3 $222.49   13.575%   $252.693   $252.69   $252.70   $252.70  
  Purchase #4 $136.82   7.463%   $147.0309   $147.03   $147.05   $147.00  
  Purchase #5 $153.79   13.207%   $174.101   $174.10   $174.10   $174.10  
  Purchase #6 $107.25   9.401%   $117.3326   $117.33   $117.35   $117.30  
  Purchase #7 $231.92   9.398%   $253.7158   $253.72   $253.70   $253.70  
  7 purchase totals = $1,022.47       $1,135.5320   $1,135.53   $1,135.55   $1,135.50