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 $241.59   4.243%   $251.8407   $251.84   $251.85   $251.80  
  Purchase #2 $225.33   9.459%   $246.644   $246.64   $246.65   $246.60  
  Purchase #3 $146.29   12.820%   $165.0444   $165.04   $165.05   $165.00  
  Purchase #4 $240.29   10.252%   $264.9245   $264.92   $264.90   $264.90  
  Purchase #5 $176.75   6.701%   $188.594   $188.59   $188.60   $188.60  
  Purchase #6 $29.46   8.818%   $32.0578   $32.06   $32.05   $32.10  
  Purchase #7 $137.92   12.744%   $155.4965   $155.50   $155.50   $155.50  
  7 purchase totals = $1,197.63       $1,304.6019   $1,304.59   $1,304.60   $1,304.50