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 $84.95   5.118%   $89.2977   $89.30   $89.30   $89.30  
  Purchase #2 $160.68   11.675%   $179.4394   $179.44   $179.45   $179.40  
  Purchase #3 $174.72   4.199%   $182.0565   $182.06   $182.05   $182.10  
  Purchase #4 $8.93   3.774%   $9.267   $9.27   $9.25   $9.30  
  Purchase #5 $149.75   6.156%   $158.9686   $158.97   $158.95   $159.00  
  Purchase #6 $214.55   4.463%   $224.1254   $224.13   $224.15   $224.10  
  Purchase #7 $169.86   8.717%   $184.6667   $184.67   $184.65   $184.70  
  7 purchase totals = $963.44       $1,027.8213   $1,027.84   $1,027.80   $1,027.90