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 $212.33   13.530%   $241.0582   $241.06   $241.05   $241.10  
  Purchase #2 $115.35   11.477%   $128.5887   $128.59   $128.60   $128.60  
  Purchase #3 $186.37   8.293%   $201.8257   $201.83   $201.85   $201.80  
  Purchase #4 $112.73   5.173%   $118.5615   $118.56   $118.55   $118.60  
  Purchase #5 $143.86   3.753%   $149.2591   $149.26   $149.25   $149.30  
  Purchase #6 $137.87   3.637%   $142.8843   $142.88   $142.90   $142.90  
  Purchase #7 $80.92   7.789%   $87.2229   $87.22   $87.20   $87.20  
  7 purchase totals = $989.43       $1,069.4004   $1,069.40   $1,069.40   $1,069.50