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 $56.37   4.835%   $59.0955   $59.10   $59.10   $59.10  
  Purchase #2 $129.70   6.547%   $138.1915   $138.19   $138.20   $138.20  
  Purchase #3 $167.55   5.274%   $176.3866   $176.39   $176.40   $176.40  
  Purchase #4 $226.66   11.748%   $253.288   $253.29   $253.30   $253.30  
  Purchase #5 $195.81   4.662%   $204.9387   $204.94   $204.95   $204.90  
  Purchase #6 $161.40   4.229%   $168.2256   $168.23   $168.25   $168.20  
  Purchase #7 $23.65   13.507%   $26.8444   $26.84   $26.85   $26.80  
  7 purchase totals = $961.14       $1,026.9703   $1,026.98   $1,027.05   $1,026.90