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 $184.25   9.647%   $202.0246   $202.02   $202.00   $202.00  
  Purchase #2 $138.75   12.255%   $155.7538   $155.75   $155.75   $155.80  
  Purchase #3 $227.82   4.783%   $238.7166   $238.72   $238.70   $238.70  
  Purchase #4 $94.77   9.812%   $104.0688   $104.07   $104.05   $104.10  
  Purchase #5 $210.76   9.443%   $230.6621   $230.66   $230.65   $230.70  
  Purchase #6 $156.71   9.357%   $171.3734   $171.37   $171.35   $171.40  
  Purchase #7 $147.82   10.732%   $163.684   $163.68   $163.70   $163.70  
  7 purchase totals = $1,160.88       $1,266.2833   $1,266.27   $1,266.20   $1,266.40