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 $118.61   4.543%   $123.9985   $124.00   $124.00   $124.00  
  Purchase #2 $174.51   7.177%   $187.0346   $187.03   $187.05   $187.00  
  Purchase #3 $160.52   3.370%   $165.9295   $165.93   $165.95   $165.90  
  Purchase #4 $231.37   6.138%   $245.5715   $245.57   $245.55   $245.60  
  Purchase #5 $103.55   4.869%   $108.5918   $108.59   $108.60   $108.60  
  Purchase #6 $89.88   8.684%   $97.6852   $97.69   $97.70   $97.70  
  Purchase #7 $182.60   13.331%   $206.9424   $206.94   $206.95   $206.90  
  7 purchase totals = $1,061.04       $1,135.7535   $1,135.75   $1,135.80   $1,135.70