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 $205.91   7.179%   $220.6923   $220.69   $220.70   $220.70  
  Purchase #2 $156.37   9.645%   $171.4519   $171.45   $171.45   $171.50  
  Purchase #3 $55.91   4.782%   $58.5836   $58.58   $58.60   $58.60  
  Purchase #4 $39.28   13.387%   $44.5384   $44.54   $44.55   $44.50  
  Purchase #5 $204.79   13.613%   $232.6681   $232.67   $232.65   $232.70  
  Purchase #6 $195.45   11.872%   $218.6538   $218.65   $218.65   $218.70  
  Purchase #7 $71.74   6.700%   $76.5466   $76.55   $76.55   $76.50  
  7 purchase totals = $929.45       $1,023.1347   $1,023.13   $1,023.15   $1,023.20