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 $184.75   5.310%   $194.5602   $194.56   $194.55   $194.60  
  Purchase #2 $65.38   4.202%   $68.1273   $68.13   $68.15   $68.10  
  Purchase #3 $94.59   12.421%   $106.339   $106.34   $106.35   $106.30  
  Purchase #4 $220.83   11.509%   $246.2453   $246.25   $246.25   $246.20  
  Purchase #5 $24.67   8.598%   $26.7911   $26.79   $26.80   $26.80  
  Purchase #6 $219.50   11.385%   $244.4901   $244.49   $244.50   $244.50  
  Purchase #7 $114.27   7.648%   $123.0094   $123.01   $123.00   $123.00  
  7 purchase totals = $923.99       $1,009.5624   $1,009.57   $1,009.60   $1,009.50