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 $212.46   10.127%   $233.9758   $233.98   $234.00   $234.00  
  Purchase #2 $151.28   3.696%   $156.8713   $156.87   $156.85   $156.90  
  Purchase #3 $119.70   9.358%   $130.9015   $130.90   $130.90   $130.90  
  Purchase #4 $16.84   6.124%   $17.8713   $17.87   $17.85   $17.90  
  Purchase #5 $194.85   12.441%   $219.0913   $219.09   $219.10   $219.10  
  Purchase #6 $141.90   4.862%   $148.7992   $148.80   $148.80   $148.80  
  Purchase #7 $188.97   7.317%   $202.7969   $202.80   $202.80   $202.80  
  7 purchase totals = $1,026.00       $1,110.3073   $1,110.31   $1,110.30   $1,110.40