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 $243.86   6.655%   $260.0889   $260.09   $260.10   $260.10  
  Purchase #2 $224.47   11.194%   $249.5972   $249.60   $249.60   $249.60  
  Purchase #3 $162.85   10.698%   $180.2717   $180.27   $180.25   $180.30  
  Purchase #4 $35.32   9.480%   $38.6683   $38.67   $38.65   $38.70  
  Purchase #5 $50.39   11.279%   $56.0735   $56.07   $56.05   $56.10  
  Purchase #6 $166.60   3.647%   $172.6759   $172.68   $172.70   $172.70  
  Purchase #7 $92.25   11.874%   $103.2038   $103.20   $103.20   $103.20  
  7 purchase totals = $975.74       $1,060.5793   $1,060.58   $1,060.55   $1,060.70