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 $10.44   12.627%   $11.7583   $11.76   $11.75   $11.80  
  Purchase #2 $153.58   8.736%   $166.9967   $167.00   $167.00   $167.00  
  Purchase #3 $33.63   12.323%   $37.7742   $37.77   $37.75   $37.80  
  Purchase #4 $209.38   12.120%   $234.7569   $234.76   $234.75   $234.80  
  Purchase #5 $196.68   5.510%   $207.5171   $207.52   $207.50   $207.50  
  Purchase #6 $175.44   3.714%   $181.9558   $181.96   $181.95   $182.00  
  Purchase #7 $224.40   6.227%   $238.3734   $238.37   $238.35   $238.40  
  7 purchase totals = $1,003.55       $1,079.1324   $1,079.14   $1,079.05   $1,079.30