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 $184.97   7.242%   $198.3655   $198.37   $198.35   $198.40  
  Purchase #2 $226.42   7.613%   $243.6574   $243.66   $243.65   $243.70  
  Purchase #3 $101.46   9.829%   $111.4325   $111.43   $111.45   $111.40  
  Purchase #4 $88.95   10.448%   $98.2435   $98.24   $98.25   $98.20  
  Purchase #5 $85.53   11.844%   $95.6602   $95.66   $95.65   $95.70  
  Purchase #6 $98.97   4.688%   $103.6097   $103.61   $103.60   $103.60  
  Purchase #7 $165.54   9.819%   $181.7944   $181.79   $181.80   $181.80  
  7 purchase totals = $951.84       $1,032.7632   $1,032.76   $1,032.75   $1,032.80