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 $187.60   9.714%   $205.8235   $205.82   $205.80   $205.80  
  Purchase #2 $26.78   6.298%   $28.4666   $28.47   $28.45   $28.50  
  Purchase #3 $192.64   9.760%   $211.4417   $211.44   $211.45   $211.40  
  Purchase #4 $58.61   5.227%   $61.6735   $61.67   $61.65   $61.70  
  Purchase #5 $249.59   10.864%   $276.7055   $276.71   $276.70   $276.70  
  Purchase #6 $23.45   4.270%   $24.4513   $24.45   $24.45   $24.50  
  Purchase #7 $144.92   5.717%   $153.2051   $153.21   $153.20   $153.20  
  7 purchase totals = $883.59       $961.7672   $961.77   $961.70   $961.80