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 $167.57   12.532%   $188.5699   $188.57   $188.55   $188.60  
  Purchase #2 $25.94   9.835%   $28.4912   $28.49   $28.50   $28.50  
  Purchase #3 $81.68   4.831%   $85.626   $85.63   $85.65   $85.60  
  Purchase #4 $181.65   11.453%   $202.4544   $202.45   $202.45   $202.50  
  Purchase #5 $203.51   10.733%   $225.3527   $225.35   $225.35   $225.40  
  Purchase #6 $206.72   6.140%   $219.4126   $219.41   $219.40   $219.40  
  Purchase #7 $96.45   9.706%   $105.8114   $105.81   $105.80   $105.80  
  7 purchase totals = $963.52       $1,055.7182   $1,055.71   $1,055.70   $1,055.80