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 $243.79   8.335%   $264.1099   $264.11   $264.10   $264.10  
  Purchase #2 $107.77   11.141%   $119.7767   $119.78   $119.80   $119.80  
  Purchase #3 $60.68   11.736%   $67.8014   $67.80   $67.80   $67.80  
  Purchase #4 $184.98   7.609%   $199.0551   $199.06   $199.05   $199.10  
  Purchase #5 $168.38   7.543%   $181.0809   $181.08   $181.10   $181.10  
  Purchase #6 $122.85   12.469%   $138.1682   $138.17   $138.15   $138.20  
  Purchase #7 $59.74   11.380%   $66.5384   $66.54   $66.55   $66.50  
  7 purchase totals = $948.19       $1,036.5306   $1,036.54   $1,036.55   $1,036.60