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 $204.47   10.321%   $225.5733   $225.57   $225.55   $225.60  
  Purchase #2 $47.60   12.280%   $53.4453   $53.45   $53.45   $53.40  
  Purchase #3 $39.58   4.347%   $41.3005   $41.30   $41.30   $41.30  
  Purchase #4 $238.92   5.419%   $251.8671   $251.87   $251.85   $251.90  
  Purchase #5 $238.44   5.578%   $251.7402   $251.74   $251.75   $251.70  
  Purchase #6 $30.96   6.193%   $32.8774   $32.88   $32.90   $32.90  
  Purchase #7 $183.72   9.453%   $201.0871   $201.09   $201.10   $201.10  
  7 purchase totals = $983.69       $1,057.8909   $1,057.90   $1,057.90   $1,057.90