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 $118.41   7.270%   $127.0184   $127.02   $127.00   $127.00  
  Purchase #2 $69.59   9.231%   $76.0139   $76.01   $76.00   $76.00  
  Purchase #3 $25.38   5.194%   $26.6982   $26.70   $26.70   $26.70  
  Purchase #4 $206.42   10.769%   $228.6494   $228.65   $228.65   $228.60  
  Purchase #5 $95.64   7.505%   $102.8178   $102.82   $102.80   $102.80  
  Purchase #6 $198.79   5.607%   $209.9362   $209.94   $209.95   $209.90  
  Purchase #7 $85.50   5.631%   $90.3145   $90.31   $90.30   $90.30  
  7 purchase totals = $799.73       $861.4484   $861.45   $861.40   $861.30