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 $8.64   4.405%   $9.0206   $9.02   $9.00   $9.00  
  Purchase #2 $20.77   13.456%   $23.5648   $23.56   $23.55   $23.60  
  Purchase #3 $144.50   11.228%   $160.7245   $160.72   $160.70   $160.70  
  Purchase #4 $128.93   12.701%   $145.3054   $145.31   $145.30   $145.30  
  Purchase #5 $121.83   10.869%   $135.0717   $135.07   $135.05   $135.10  
  Purchase #6 $238.45   6.760%   $254.5692   $254.57   $254.55   $254.60  
  Purchase #7 $13.75   7.515%   $14.7833   $14.78   $14.80   $14.80  
  7 purchase totals = $676.87       $743.0395   $743.03   $742.95   $743.10