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 $219.79   12.276%   $246.7714   $246.77   $246.75   $246.80  
  Purchase #2 $165.74   5.234%   $174.4148   $174.41   $174.40   $174.40  
  Purchase #3 $18.62   3.646%   $19.2989   $19.30   $19.30   $19.30  
  Purchase #4 $84.79   11.522%   $94.5595   $94.56   $94.55   $94.60  
  Purchase #5 $181.89   11.496%   $202.8001   $202.80   $202.80   $202.80  
  Purchase #6 $99.93   13.704%   $113.6244   $113.62   $113.60   $113.60  
  Purchase #7 $179.38   6.130%   $190.376   $190.38   $190.40   $190.40  
  7 purchase totals = $950.14       $1,041.8451   $1,041.84   $1,041.80   $1,041.90