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 $212.57   10.615%   $235.1343   $235.13   $235.15   $235.10  
  Purchase #2 $148.83   7.849%   $160.5117   $160.51   $160.50   $160.50  
  Purchase #3 $154.84   6.162%   $164.3812   $164.38   $164.40   $164.40  
  Purchase #4 $174.59   9.146%   $190.558   $190.56   $190.55   $190.60  
  Purchase #5 $147.67   5.423%   $155.6781   $155.68   $155.70   $155.70  
  Purchase #6 $157.65   8.449%   $170.9698   $170.97   $170.95   $171.00  
  Purchase #7 $52.86   9.205%   $57.7258   $57.73   $57.75   $57.70  
  7 purchase totals = $1,049.01       $1,134.9589   $1,134.96   $1,135.00   $1,135.00