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 $210.82   9.383%   $230.6012   $230.60   $230.60   $230.60  
  Purchase #2 $197.84   9.342%   $216.3222   $216.32   $216.30   $216.30  
  Purchase #3 $232.36   5.235%   $244.524   $244.52   $244.50   $244.50  
  Purchase #4 $164.45   11.157%   $182.7977   $182.80   $182.80   $182.80  
  Purchase #5 $159.94   5.586%   $168.8742   $168.87   $168.85   $168.90  
  Purchase #6 $179.30   12.482%   $201.6802   $201.68   $201.70   $201.70  
  Purchase #7 $23.43   11.254%   $26.0668   $26.07   $26.05   $26.10  
  7 purchase totals = $1,168.14       $1,270.8663   $1,270.86   $1,270.80   $1,270.90