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 $91.51   13.353%   $103.7293   $103.73   $103.75   $103.70  
  Purchase #2 $220.33   9.643%   $241.5764   $241.58   $241.60   $241.60  
  Purchase #3 $123.95   9.563%   $135.8033   $135.80   $135.80   $135.80  
  Purchase #4 $43.83   4.437%   $45.7747   $45.77   $45.75   $45.80  
  Purchase #5 $41.25   12.115%   $46.2474   $46.25   $46.25   $46.20  
  Purchase #6 $244.62   12.343%   $274.8134   $274.81   $274.80   $274.80  
  Purchase #7 $31.69   5.401%   $33.4016   $33.40   $33.40   $33.40  
  7 purchase totals = $797.18       $881.3461   $881.34   $881.35   $881.30