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 $110.96   7.264%   $119.0201   $119.02   $119.00   $119.00  
  Purchase #2 $51.33   12.732%   $57.8653   $57.87   $57.85   $57.90  
  Purchase #3 $12.74   6.401%   $13.5555   $13.56   $13.55   $13.60  
  Purchase #4 $195.44   12.802%   $220.4602   $220.46   $220.45   $220.50  
  Purchase #5 $190.67   11.315%   $212.2443   $212.24   $212.25   $212.20  
  Purchase #6 $118.37   7.368%   $127.0915   $127.09   $127.10   $127.10  
  Purchase #7 $238.47   5.406%   $251.3617   $251.36   $251.35   $251.40  
  7 purchase totals = $917.98       $1,001.5986   $1,001.60   $1,001.55   $1,001.70