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 $105.35   7.286%   $113.0258   $113.03   $113.05   $113.00  
  Purchase #2 $243.80   7.402%   $261.8461   $261.85   $261.85   $261.80  
  Purchase #3 $98.81   4.195%   $102.9551   $102.96   $102.95   $103.00  
  Purchase #4 $211.34   6.861%   $225.84   $225.84   $225.85   $225.80  
  Purchase #5 $175.41   12.143%   $196.71   $196.71   $196.70   $196.70  
  Purchase #6 $145.57   7.165%   $156.0001   $156.00   $156.00   $156.00  
  Purchase #7 $31.37   3.162%   $32.3619   $32.36   $32.35   $32.40  
  7 purchase totals = $1,011.65       $1,088.7390   $1,088.75   $1,088.75   $1,088.70