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 $55.45   9.121%   $60.5076   $60.51   $60.50   $60.50  
  Purchase #2 $201.34   12.580%   $226.6686   $226.67   $226.65   $226.70  
  Purchase #3 $220.65   9.379%   $241.3448   $241.34   $241.35   $241.30  
  Purchase #4 $36.53   12.507%   $41.0988   $41.10   $41.10   $41.10  
  Purchase #5 $121.60   7.298%   $130.4744   $130.47   $130.45   $130.50  
  Purchase #6 $172.32   12.543%   $193.9341   $193.93   $193.95   $193.90  
  Purchase #7 $170.97   6.613%   $182.2762   $182.28   $182.30   $182.30  
  7 purchase totals = $978.86       $1,076.3045   $1,076.30   $1,076.30   $1,076.30