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 $238.89   11.835%   $267.1626   $267.16   $267.15   $267.20  
  Purchase #2 $83.60   3.819%   $86.7927   $86.79   $86.80   $86.80  
  Purchase #3 $113.62   6.210%   $120.6758   $120.68   $120.70   $120.70  
  Purchase #4 $228.58   11.231%   $254.2518   $254.25   $254.25   $254.30  
  Purchase #5 $109.95   3.283%   $113.5597   $113.56   $113.55   $113.60  
  Purchase #6 $87.45   9.588%   $95.8347   $95.83   $95.85   $95.80  
  Purchase #7 $82.80   11.523%   $92.341   $92.34   $92.35   $92.30  
  7 purchase totals = $944.89       $1,030.6183   $1,030.61   $1,030.65   $1,030.70