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 $193.57   4.589%   $202.4529   $202.45   $202.45   $202.50  
  Purchase #2 $87.67   11.680%   $97.9099   $97.91   $97.90   $97.90  
  Purchase #3 $116.84   13.111%   $132.1589   $132.16   $132.15   $132.20  
  Purchase #4 $59.79   3.133%   $61.6632   $61.66   $61.65   $61.70  
  Purchase #5 $110.65   12.425%   $124.3983   $124.40   $124.40   $124.40  
  Purchase #6 $226.31   9.201%   $247.1328   $247.13   $247.15   $247.10  
  Purchase #7 $189.60   6.435%   $201.8008   $201.80   $201.80   $201.80  
  7 purchase totals = $984.43       $1,067.5168   $1,067.51   $1,067.50   $1,067.60