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 $207.57   9.698%   $227.7001   $227.70   $227.70   $227.70  
  Purchase #2 $248.80   6.244%   $264.3351   $264.34   $264.35   $264.30  
  Purchase #3 $53.80   10.558%   $59.4802   $59.48   $59.50   $59.50  
  Purchase #4 $78.60   12.232%   $88.2144   $88.21   $88.20   $88.20  
  Purchase #5 $118.44   5.765%   $125.2681   $125.27   $125.25   $125.30  
  Purchase #6 $161.88   6.435%   $172.297   $172.30   $172.30   $172.30  
  Purchase #7 $102.59   10.306%   $113.1629   $113.16   $113.15   $113.20  
  7 purchase totals = $971.68       $1,050.4578   $1,050.46   $1,050.45   $1,050.50