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 $135.80   11.624%   $151.5854   $151.59   $151.60   $151.60  
  Purchase #2 $245.73   12.503%   $276.4536   $276.45   $276.45   $276.50  
  Purchase #3 $16.50   9.144%   $18.0088   $18.01   $18.00   $18.00  
  Purchase #4 $121.37   9.719%   $133.166   $133.17   $133.15   $133.20  
  Purchase #5 $243.94   12.670%   $274.8472   $274.85   $274.85   $274.80  
  Purchase #6 $150.87   6.506%   $160.6856   $160.69   $160.70   $160.70  
  Purchase #7 $10.58   3.550%   $10.9556   $10.96   $10.95   $11.00  
  7 purchase totals = $924.79       $1,025.7022   $1,025.72   $1,025.70   $1,025.80