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 $93.34   3.175%   $96.3035   $96.30   $96.30   $96.30  
  Purchase #2 $248.84   11.355%   $277.0958   $277.10   $277.10   $277.10  
  Purchase #3 $38.50   8.463%   $41.7583   $41.76   $41.75   $41.80  
  Purchase #4 $210.83   3.323%   $217.8359   $217.84   $217.85   $217.80  
  Purchase #5 $228.32   9.783%   $250.6565   $250.66   $250.65   $250.70  
  Purchase #6 $72.83   11.594%   $81.2739   $81.27   $81.25   $81.30  
  Purchase #7 $113.86   13.224%   $128.9168   $128.92   $128.90   $128.90  
  7 purchase totals = $1,006.52       $1,093.8407   $1,093.85   $1,093.80   $1,093.90