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 $84.47   11.323%   $94.0345   $94.03   $94.05   $94.00  
  Purchase #2 $142.44   12.605%   $160.3946   $160.39   $160.40   $160.40  
  Purchase #3 $138.51   8.829%   $150.739   $150.74   $150.75   $150.70  
  Purchase #4 $177.42   6.238%   $188.4875   $188.49   $188.50   $188.50  
  Purchase #5 $96.53   8.853%   $105.0758   $105.08   $105.10   $105.10  
  Purchase #6 $189.93   12.688%   $214.0283   $214.03   $214.05   $214.00  
  Purchase #7 $117.39   9.528%   $128.5749   $128.57   $128.55   $128.60  
  7 purchase totals = $946.69       $1,041.3346   $1,041.33   $1,041.40   $1,041.30