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 $174.91   5.544%   $184.607   $184.61   $184.60   $184.60  
  Purchase #2 $123.53   6.824%   $131.9597   $131.96   $131.95   $132.00  
  Purchase #3 $126.83   13.378%   $143.7973   $143.80   $143.80   $143.80  
  Purchase #4 $191.27   5.264%   $201.3385   $201.34   $201.35   $201.30  
  Purchase #5 $239.83   3.170%   $247.4326   $247.43   $247.45   $247.40  
  Purchase #6 $79.48   5.500%   $83.8514   $83.85   $83.85   $83.90  
  Purchase #7 $127.60   8.613%   $138.5902   $138.59   $138.60   $138.60  
  7 purchase totals = $1,063.45       $1,131.5767   $1,131.58   $1,131.60   $1,131.60