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 $182.97   10.560%   $202.2916   $202.29   $202.30   $202.30  
  Purchase #2 $144.69   13.333%   $163.9815   $163.98   $164.00   $164.00  
  Purchase #3 $174.79   5.620%   $184.6132   $184.61   $184.60   $184.60  
  Purchase #4 $227.82   10.563%   $251.8846   $251.88   $251.90   $251.90  
  Purchase #5 $68.60   8.219%   $74.2382   $74.24   $74.25   $74.20  
  Purchase #6 $137.50   13.158%   $155.5923   $155.59   $155.60   $155.60  
  Purchase #7 $119.52   4.753%   $125.2008   $125.20   $125.20   $125.20  
  7 purchase totals = $1,055.89       $1,157.8022   $1,157.79   $1,157.85   $1,157.80