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 $193.40   4.848%   $202.776   $202.78   $202.80   $202.80  
  Purchase #2 $27.27   8.600%   $29.6152   $29.62   $29.60   $29.60  
  Purchase #3 $150.98   10.488%   $166.8148   $166.81   $166.80   $166.80  
  Purchase #4 $96.58   11.832%   $108.0073   $108.01   $108.00   $108.00  
  Purchase #5 $250.25   7.200%   $268.268   $268.27   $268.25   $268.30  
  Purchase #6 $229.80   10.526%   $253.9887   $253.99   $254.00   $254.00  
  Purchase #7 $30.81   4.755%   $32.275   $32.28   $32.30   $32.30  
  7 purchase totals = $979.09       $1,061.7450   $1,061.76   $1,061.75   $1,061.80