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 $108.81   12.755%   $122.6887   $122.69   $122.70   $122.70  
  Purchase #2 $50.62   9.692%   $55.5261   $55.53   $55.55   $55.50  
  Purchase #3 $85.94   13.831%   $97.8264   $97.83   $97.85   $97.80  
  Purchase #4 $186.98   3.210%   $192.9821   $192.98   $193.00   $193.00  
  Purchase #5 $59.79   13.445%   $67.8288   $67.83   $67.85   $67.80  
  Purchase #6 $233.80   6.600%   $249.2308   $249.23   $249.25   $249.20  
  Purchase #7 $216.66   13.845%   $246.6566   $246.66   $246.65   $246.70  
  7 purchase totals = $942.60       $1,032.7395   $1,032.75   $1,032.85   $1,032.70