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 $41.52   13.317%   $47.0492   $47.05   $47.05   $47.00  
  Purchase #2 $165.56   9.162%   $180.7286   $180.73   $180.75   $180.70  
  Purchase #3 $235.88   11.747%   $263.5888   $263.59   $263.60   $263.60  
  Purchase #4 $192.32   3.819%   $199.6647   $199.66   $199.65   $199.70  
  Purchase #5 $243.41   7.231%   $261.011   $261.01   $261.00   $261.00  
  Purchase #6 $204.30   11.455%   $227.7026   $227.70   $227.70   $227.70  
  Purchase #7 $129.90   13.841%   $147.8795   $147.88   $147.90   $147.90  
  7 purchase totals = $1,212.89       $1,327.6244   $1,327.62   $1,327.65   $1,327.60