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 $54.97   8.873%   $59.8475   $59.85   $59.85   $59.80  
  Purchase #2 $74.43   13.678%   $84.6105   $84.61   $84.60   $84.60  
  Purchase #3 $196.57   7.487%   $211.2872   $211.29   $211.30   $211.30  
  Purchase #4 $233.26   6.187%   $247.6918   $247.69   $247.70   $247.70  
  Purchase #5 $159.37   9.602%   $174.6727   $174.67   $174.65   $174.70  
  Purchase #6 $179.64   4.531%   $187.7795   $187.78   $187.80   $187.80  
  Purchase #7 $112.82   4.747%   $118.1756   $118.18   $118.20   $118.20  
  7 purchase totals = $1,011.06       $1,084.0648   $1,084.07   $1,084.10   $1,084.10