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 $94.93   3.873%   $98.6066   $98.61   $98.60   $98.60  
  Purchase #2 $223.45   5.221%   $235.1163   $235.12   $235.10   $235.10  
  Purchase #3 $173.77   3.114%   $179.1812   $179.18   $179.20   $179.20  
  Purchase #4 $181.66   11.629%   $202.7852   $202.79   $202.80   $202.80  
  Purchase #5 $162.67   7.145%   $174.2928   $174.29   $174.30   $174.30  
  Purchase #6 $174.30   7.656%   $187.6444   $187.64   $187.65   $187.60  
  Purchase #7 $173.75   8.586%   $188.6682   $188.67   $188.65   $188.70  
  7 purchase totals = $1,184.53       $1,266.2947   $1,266.30   $1,266.30   $1,266.30